Fixes implementation of `explainedVariance` and `r2` to be consistent with their definitions as described in [SPARK-9005](https://issues.apache.org/jira/browse/SPARK-9005).

Author: Feynman Liang <fliang@databricks.com>

Closes #7361 from feynmanliang/SPARK-9005-RegressionMetrics-bugs and squashes the following commits:

f1112fc [Feynman Liang] Add explainedVariance formula
1a3d098 [Feynman Liang] SROwen code review comments
08a0e1b [Feynman Liang] Fix pyspark tests
db8605a [Feynman Liang] Style fix
bde9761 [Feynman Liang] Fix RegressionMetrics tests, relax assumption predictor is unbiased
c235de0 [Feynman Liang] Fix RegressionMetrics tests
4c4e56f [Feynman Liang] Fix RegressionMetrics computation of explainedVariance and r2

Add confusionMatrix method at class MulticlassMetrics in pyspark/mllib

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #7286 from yanboliang/spark-8068 and squashes the following commits:

6109fe1 [Yanbo Liang] Add confusionMatrix method at class MulticlassMetrics in pyspark/mllib

Check then make the MLlib Python evaluation and feature doc to be as complete as the Scala doc.

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #6461 from yanboliang/spark-7918 and squashes the following commits:

940e3f1 [Yanbo Liang] truncate too long line and remove extra sparse
a80ae58 [Yanbo Liang] MLlib Python doc parity check for evaluation and feature

Add MultilabelMetrics in PySpark/MLlib

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #6276 from yanboliang/spark-6094 and squashes the following commits:

b8e3343 [Yanbo Liang] Add MultilabelMetrics in PySpark/MLlib

Fixed the following warnings in `make clean html` under `python/docs`:

~~~
/Users/meng/src/spark/python/pyspark/mllib/evaluation.py:docstring of pyspark.mllib.evaluation.RankingMetrics.ndcgAt:3: ERROR: Unexpected indentation.
/Users/meng/src/spark/python/pyspark/mllib/evaluation.py:docstring of pyspark.mllib.evaluation.RankingMetrics.ndcgAt:4: WARNING: Block quote ends without a blank line; unexpected unindent.
/Users/meng/src/spark/python/pyspark/mllib/fpm.py:docstring of pyspark.mllib.fpm.FPGrowth.train:3: ERROR: Unexpected indentation.
/Users/meng/src/spark/python/pyspark/mllib/fpm.py:docstring of pyspark.mllib.fpm.FPGrowth.train:4: WARNING: Block quote ends without a blank line; unexpected unindent.
/Users/meng/src/spark/python/pyspark/sql/__init__.py:docstring of pyspark.sql.DataFrame.replace:16: WARNING: Field list ends without a blank line; unexpected unindent.
/Users/meng/src/spark/python/pyspark/streaming/kafka.py:docstring of pyspark.streaming.kafka.KafkaUtils.createRDD:8: ERROR: Unexpected indentation.
/Users/meng/src/spark/python/pyspark/streaming/kafka.py:docstring of pyspark.streaming.kafka.KafkaUtils.createRDD:9: WARNING: Block quote ends without a blank line; unexpected unindent.
~~~

davies

Author: Xiangrui Meng <meng@databricks.com>

Closes #6221 from mengxr/SPARK-6657 and squashes the following commits:

e3f83fe [Xiangrui Meng] fix sql and streaming doc warnings
2b4371e [Xiangrui Meng] fix mllib python doc warnings

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #6044 from yanboliang/spark-6092 and squashes the following commits:

726a9b1 [Yanbo Liang] add newRankingMetrics
33f649c [Yanbo Liang] Add RankingMetrics in PySpark/MLlib

https://issues.apache.org/jira/browse/SPARK-6091

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #6011 from yanboliang/spark-6091 and squashes the following commits:

bb3e4ba [Yanbo Liang] trigger jenkins
53c045d [Yanbo Liang] keep compatibility for python 2.6
972d5ac [Yanbo Liang] Add MulticlassMetrics in PySpark/MLlib

https://issues.apache.org/jira/browse/SPARK-6093

Author: Yanbo Liang <ybliang8@gmail.com>

Closes #5941 from yanboliang/spark-6093 and squashes the following commits:

6934af3 [Yanbo Liang] change to @property
aac3bc5 [Yanbo Liang] Add RegressionMetrics in PySpark/MLlib

A simple wrapper around the Scala implementation. `DataFrame` is used for serialization/deserialization. Methods that return `RDD`s are not supported in this PR.

davies If we recognize Scala's `Product`s in Py4J, we can easily add wrappers for Scala methods that returns `RDD[(Double, Double)]`. Is it easy to register serializer for `Product` in PySpark?

Author: Xiangrui Meng <meng@databricks.com>

Closes #4863 from mengxr/SPARK-6090 and squashes the following commits:

009a3a3 [Xiangrui Meng] provide schema
dcddab5 [Xiangrui Meng] add a basic BinaryClassificationMetrics to PySpark/MLlib