Add sample scraping/automation example via Phantomjs

Signed-off-by: Alex Ellis <alexellis2@gmail.com>

sample-functions/Phantomjs/Dockerfile

+FROM alexellis2/phantomjs-docker:latest
+
+ADD https://github.com/alexellis/faas/releases/download/0.5.6-alpha/fwatchdog /usr/bin
+RUN chmod +x /usr/bin/fwatchdog
+
+ENV fprocess="phantomjs /dev/stdin"
+
+HEALTHCHECK --interval=5s CMD [ -e /tmp/.lock ] || exit 1
+CMD ["fwatchdog"]

sample-functions/Phantomjs/README.md

+### Phantomjs function
+
+[Phantomjs](http://phantomjs.org) is a headless web-browser used for scraping and automation testing. This function will scrape a web-page with the JavaScript sent in through the function.
+
+Example usage:
+
+```
+$ time curl --data-binary @cnn.js http://localhost:8080/function/phantomjs
+
+Status: success
+CNN - Breaking News, Latest News and Videos
+
+real    0m8.729s
+```
+
+This script visits the front page of CNN and once it is fully loaded - scrapes the title.
+
+See [cnn.js](https://github.com/alexellis/faas/tree/master/sample-functions/Phantomjs/cnn.js) as an example of a Phantomjs script.
+
+Another example script [feedly_subscribers.js](https://github.com/alexellis/faas/tree/master/sample-functions/Phantomjs/feedly_subscribers.js) gives the count of subscribers for an RSS Feed registered on Feedly.
+

sample-functions/Phantomjs/cnn.js

+var webPage = require('webpage');
+var page = webPage.create();
+
+page.open('https://www.cnn.com/', function(status) {
+  console.log('Status: ' + status);
+  console.log(page.title);
+  // Do other things here...
+  phantom.exit();
+
+});

sample-functions/Phantomjs/feedly_subscribers.js

+var webPage = require('webpage');
+var page = webPage.create();
+
+var feed = "http://blog.alexellis.io/rss/";
+var url = "https://feedly.com/i/subscription/feed/" + feed;
+
+page.open(url, function(status) {
+  var title = page.evaluate(function(s) {
+    return document.querySelector(s).innerText;
+  }, ".count-followers");
+  console.log(title.split(" ")[0]);
+  phantom.exit();
+});