[SPARK-7557] [ML] [DOC] User guide for spark.ml HashingTF, Tokenizer

Added feature transformer subsection to spark.ml guide, with HashingTF and Tokenizer.  Added JavaHashingTFSuite to test Java examples in new guide.

I've run Scala, Python examples in the Spark/PySpark shells.  I ran the Java examples via the test suite (with small modifications for printing).

CC: mengxr

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

Closes #6093 from jkbradley/hashingtf-guide and squashes the following commits:

d5d213f [Joseph K. Bradley] small fix
dd6e91a [Joseph K. Bradley] fixes from code review of user guide
33c3ff9 [Joseph K. Bradley] small fix
bc6058c [Joseph K. Bradley] fix link
361a174 [Joseph K. Bradley] Added subsection for feature transformers to spark.ml guide, with HashingTF and Tokenizer.  Added JavaHashingTFSuite to test Java examples in new guide