[SPARK-8353] [DOCS] Show anchor links when hovering over documentation headers

This patch uses [AnchorJS](https://bryanbraun.github.io/anchorjs/) to show deep anchor links when hovering over headers in the Spark documentation. For example:

![image](https://cloud.githubusercontent.com/assets/50748/8240800/1502f85c-15ba-11e5-819a-97b231370a39.png)

This makes it easier for users to link to specific sections of the documentation.

I also removed some dead Javascript which isn't used in our current docs (it was introduced for the old AMPCamp training, but isn't used anymore).

Author: Josh Rosen <joshrosen@databricks.com>

Closes #6808 from JoshRosen/SPARK-8353 and squashes the following commits:

e59d8a7 [Josh Rosen] Suppress underline on hover
f518b6a [Josh Rosen] Turn on for all headers, since we use H1s in a bunch of places
a9fec01 [Josh Rosen] Add anchor links when hovering over headers; remove some dead JS code

LICENSE

@@ -950,3 +950,4 @@ The following components are provided under the MIT License. See project link fo
      (MIT License) scopt (com.github.scopt:scopt_2.10:3.2.0 - https://github.com/scopt/scopt)
      (The MIT License) Mockito (org.mockito:mockito-all:1.8.5 - http://www.mockito.org)
      (MIT License) jquery (https://jquery.org/license/)
+     (MIT License) AnchorJS (https://github.com/bryanbraun/anchorjs)

docs/_layouts/global.html

@@ -138,6 +138,7 @@
 
         <script src="js/vendor/jquery-1.8.0.min.js"></script>
         <script src="js/vendor/bootstrap.min.js"></script>
+        <script src="js/vendor/anchor.min.js"></script>
         <script src="js/main.js"></script>
 
         <!-- MathJax Section -->

docs/css/main.css

@@ -146,3 +146,8 @@ ul.nav li.dropdown ul.dropdown-menu li.dropdown-submenu ul.dropdown-menu {
 .MathJax .mi { color: inherit }
 .MathJax .mf { color: inherit }
 .MathJax .mh { color: inherit }
+
+/**
+ * AnchorJS (anchor links when hovering over headers)
+ */
+a.anchorjs-link:hover { text-decoration: none; }

docs/js/main.js

@@ -68,38 +68,11 @@ function codeTabs() {
   });
 }
 
-function makeCollapsable(elt, accordionClass, accordionBodyId, title) {
-  $(elt).addClass("accordion-inner");
-  $(elt).wrap('<div class="accordion ' + accordionClass + '"></div>')
-  $(elt).wrap('<div class="accordion-group"></div>')
-  $(elt).wrap('<div id="' + accordionBodyId + '" class="accordion-body collapse"></div>')
-  $(elt).parent().before(
-    '<div class="accordion-heading">' +
-      '<a class="accordion-toggle" data-toggle="collapse" href="#' + accordionBodyId + '">' +
-             title +
-      '</a>' +
-    '</div>'
-  );
-}
-
-// Enable "view solution" sections (for exercises)
-function viewSolution() {
-  var counter = 0
-  $("div.solution").each(function() {
-    var id = "solution_" + counter
-    makeCollapsable(this, "", id,
-      '<i class="icon-ok-sign" style="text-decoration: none; color: #0088cc">' +
-      '</i>' + "View Solution");
-    counter++;
-  });
-}
 
 // A script to fix internal hash links because we have an overlapping top bar.
 // Based on https://github.com/twitter/bootstrap/issues/193#issuecomment-2281510
 function maybeScrollToHash() {
-  console.log("HERE");
   if (window.location.hash && $(window.location.hash).length) {
-    console.log("HERE2", $(window.location.hash), $(window.location.hash).offset().top);
     var newTop = $(window.location.hash).offset().top - 57;
     $(window).scrollTop(newTop);
   }
@@ -107,7 +80,12 @@ function maybeScrollToHash() {
 
 $(function() {
   codeTabs();
-  viewSolution();
+  // Display anchor links when hovering over headers. For documentation of the
+  // configuration options, see the AnchorJS documentation.
+  anchors.options = {
+    placement: 'left'
+  };
+  anchors.add();
 
   $(window).bind('hashchange', function() {
     maybeScrollToHash();

docs/js/vendor/anchor.min.js

+/*!
+ * AnchorJS - v1.1.1 - 2015-05-23
+ * https://github.com/bryanbraun/anchorjs
+ * Copyright (c) 2015 Bryan Braun; Licensed MIT
+ */
+function AnchorJS(A){"use strict";this.options=A||{},this._applyRemainingDefaultOptions=function(A){this.options.icon=this.options.hasOwnProperty("icon")?A.icon:"&#xe9cb",this.options.visible=this.options.hasOwnProperty("visible")?A.visible:"hover",this.options.placement=this.options.hasOwnProperty("placement")?A.placement:"right",this.options.class=this.options.hasOwnProperty("class")?A.class:""},this._applyRemainingDefaultOptions(A),this.add=function(A){var e,t,o,n,i,s,a,l,c,r,h,g,B,Q;if(this._applyRemainingDefaultOptions(this.options),A){if("string"!=typeof A)throw new Error("The selector provided to AnchorJS was invalid.")}else A="h1, h2, h3, h4, h5, h6";if(e=document.querySelectorAll(A),0===e.length)return!1;for(this._addBaselineStyles(),t=document.querySelectorAll("[id]"),o=[].map.call(t,function(A){return A.id}),i=0;i<e.length;i++){if(e[i].hasAttribute("id"))n=e[i].getAttribute("id");else{s=e[i].textContent,a=s.replace(/[^\w\s-]/gi,"").replace(/\s+/g,"-").replace(/-{2,}/g,"-").substring(0,64).replace(/^-+|-+$/gm,"").toLowerCase(),r=a,c=0;do void 0!==l&&(r=a+"-"+c),l=o.indexOf(r),c+=1;while(-1!==l);l=void 0,o.push(r),e[i].setAttribute("id",r),n=r}h=n.replace(/-/g," "),g='<a class="anchorjs-link '+this.options.class+'" href="#'+n+'" aria-label="Anchor link for: '+h+'" data-anchorjs-icon="'+this.options.icon+'"></a>',B=document.createElement("div"),B.innerHTML=g,Q=B.childNodes,"always"===this.options.visible&&(Q[0].style.opacity="1"),"&#xe9cb"===this.options.icon&&(Q[0].style.fontFamily="anchorjs-icons",Q[0].style.fontStyle="normal",Q[0].style.fontVariant="normal",Q[0].style.fontWeight="normal"),"left"===this.options.placement?(Q[0].style.position="absolute",Q[0].style.marginLeft="-1em",Q[0].style.paddingRight="0.5em",e[i].insertBefore(Q[0],e[i].firstChild)):(Q[0].style.paddingLeft="0.375em",e[i].appendChild(Q[0]))}return this},this.remove=function(A){for(var e,t=document.querySelectorAll(A),o=0;o<t.length;o++)e=t[o].querySelector(".anchorjs-link"),e&&t[o].removeChild(e);return this},this._addBaselineStyles=function(){if(null===document.head.querySelector("style.anchorjs")){var A,e=document.createElement("style"),t=" .anchorjs-link {   opacity: 0;   text-decoration: none;   -webkit-font-smoothing: antialiased;   -moz-osx-font-smoothing: grayscale; }",o=" *:hover > .anchorjs-link, .anchorjs-link:focus  {   opacity: 1; }",n=' @font-face {   font-family: "anchorjs-icons";   font-style: normal;   font-weight: normal;   src: url(data:application/x-font-ttf;charset=utf-8;base64,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) format("truetype"); }',i=" [data-anchorjs-icon]::after {   content: attr(data-anchorjs-icon); }";e.className="anchorjs",e.appendChild(document.createTextNode("")),A=document.head.querySelector('[rel="stylesheet"], style'),void 0===A?document.head.appendChild(e):document.head.insertBefore(e,A),e.sheet.insertRule(t,e.sheet.cssRules.length),e.sheet.insertRule(o,e.sheet.cssRules.length),e.sheet.insertRule(i,e.sheet.cssRules.length),e.sheet.insertRule(n,e.sheet.cssRules.length)}}}var anchors=new AnchorJS;