## What changes were proposed in this pull request?

Made DataFrame-based API primary
* Spark doc menu bar and other places now link to ml-guide.html, not mllib-guide.html
* mllib-guide.html keeps RDD-specific list of features, with a link at the top redirecting people to ml-guide.html
* ml-guide.html includes a "maintenance mode" announcement about the RDD-based API
  * **Reviewers: please check this carefully**
* (minor) Titles for DF API no longer include "- spark.ml" suffix.  Titles for RDD API have "- RDD-based API" suffix
* Moved migration guide to ml-guide from mllib-guide
  * Also moved past guides from mllib-migration-guides to ml-migration-guides, with a redirect link on mllib-migration-guides
  * **Reviewers**: I did not change any of the content of the migration guides.

Reorganized DataFrame-based guide:
* ml-guide.html mimics the old mllib-guide.html page in terms of content: overview, migration guide, etc.
* Moved Pipeline description into ml-pipeline.html and moved tuning into ml-tuning.html
  * **Reviewers**: I did not change the content of these guides, except some intro text.
* Sidebar remains the same, but with pipeline and tuning sections added

Other:
* ml-classification-regression.html: Moved text about linear methods to new section in page

## How was this patch tested?

Generated docs locally

Author: Joseph K. Bradley <joseph@databricks.com>

Closes #14213 from jkbradley/ml-guide-2.0.

## What changes were proposed in this pull request?
1, del precision,recall in  `ml.MulticlassClassificationEvaluator`
2, update user guide for `mlllib.weightedFMeasure`

## How was this patch tested?
local build

Author: Ruifeng Zheng <ruifengz@foxmail.com>

Closes #13390 from zhengruifeng/clarify_f1.

## What changes were proposed in this pull request?

This PR tries to fix all typos in all markdown files under `docs` module,
and fixes similar typos in other comments, too.

## How was the this patch tested?

manual tests.

Author: Dongjoon Hyun <dongjoon@apache.org>

Closes #11300 from dongjoon-hyun/minor_fix_typos.

[SPARK-12212][ML][DOC] Clarifies the difference between spark.ml, spark.mllib and mllib in the documentation.

Replaces a number of occurences of `MLlib` in the documentation that were meant to refer to the `spark.mllib` package instead. It should clarify for new users the difference between `spark.mllib` (the package) and MLlib (the umbrella project for ML in spark).

It also removes some files that I forgot to delete with #10207

Author: Timothy Hunter <timhunter@databricks.com>

Closes #10234 from thunterdb/12212.

Author: Vikas Nelamangala <vikasnelamangala@Vikass-MacBook-Pro.local>

Closes #9689 from vikasnp/master.

Recall by threshold snippet was using "precisionByThreshold"

Author: Mageswaran.D <mageswaran1989@gmail.com>

Closes #9333 from Mageswaran1989/Typo_in_mllib-evaluation-metrics.md.

In the Markdown docs for the spark.mllib Programming Guide, we have code examples with codetabs for each language. We should link to each language's API docs within the corresponding codetab, but we are inconsistent about this. For an example of what we want to do, see the "ChiSqSelector" section in https://github.com/apache/spark/blob/64743870f23bffb8d96dcc8a0181c1452782a151/docs/mllib-feature-extraction.md
This JIRA is just for spark.mllib, not spark.ml.

Please let me know if more work is needed, thanks a lot.

Author: Xin Ren <iamshrek@126.com>

Closes #8977 from keypointt/SPARK-10669.

[SPARK-9490] [DOCS] [MLLIB] MLlib evaluation metrics guide example python code uses deprecated print statement

Use print(x) not print x for Python 3 in eval examples
CC sethah mengxr -- just wanted to close this out before 1.5

Author: Sean Owen <sowen@cloudera.com>

Closes #7822 from srowen/SPARK-9490 and squashes the following commits:

01abeba [Sean Owen] Change "print x" to "print(x)" in the rest of the docs too
bd7f7fb [Sean Owen] Use print(x) not print x for Python 3 in eval examples

Author: sethah <seth.hendrickson16@gmail.com>

Closes #7655 from sethah/Working_on_6129 and squashes the following commits:

253db2d [sethah] removed number formatting from example code
b769cab [sethah] rewording threshold section
d5dad4d [sethah] adding some explanations of concepts to the eval metrics user guide
3a61ff9 [sethah] Removing unnecessary latex commands from metrics guide
c9dd058 [sethah] Cleaning up and formatting metrics user guide section
6f31c21 [sethah] All example code for metrics section done
98813fe [sethah] Most java and python example code added. Further latex formatting
53a24fc [sethah] Adding documentations of metrics for ML algorithms to user guide