[SPARK-9846] [Docs] User guide for Multilayer Perceptron Classifier

[avulanov]

Added user guide for multilayer perceptron classifier:

• Simplified description of the multilayer perceptron classifier
• Example code for Scala and Java

[SparkQA]

Test build #41084 has finished for PR 8262 at commit 96683ce.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[mengxr]

Use MulticlassClassificationEvaluator instead.

[avulanov]

@mengxr Thank you for your comments! I've addressed everything except the full chop of setters for the Java trainer. It complains on java: incompatible types: org.apache.spark.ml.classification.MultilayerPerceptronParams cannot be converted to org.apache.spark.ml.classification.MultilayerPerceptronClassifier. I did it in two stages. Also I've left Java imports.

[avulanov]

The test fail seems unrelated to my commit.

[mengxr]

Ah, that is a bug I overlooked in review. We must define setters in the final class so the return type in Java is the self type. I will send a PR for it and ping you back.

[mengxr]

use 2-space indentation (and please fix indentation in other places)

[mengxr]

LGTM except some indentation issues.

[avulanov]

@mengxr Thank you. Fixed indentation and removed trainer. Java example works now.

[SparkQA]

Test build #41335 has finished for PR 8262 at commit 07ada2b.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[mengxr]

Merged into master and branch-1.5. Thanks!