[SPARK-1285] Backporting updates to streaming docs to branch 0.9

Cherrypicked updates that have been added to master branch

Author: Aaron Kimball <aaron@magnify.io>
Author: Tathagata Das <tathagata.das1565@gmail.com>
Author: Chen Chao <crazyjvm@gmail.com>
Author: Andrew Or <andrewor14@gmail.com>

Closes #183 from tdas/branch-0.9-streaming-docs and squashes the following commits:

e1a988f [Tathagata Das] Added clean to run-tests
98c3e98 [Tathagata Das] Merge remote-tracking branch 'apache-github/branch-0.9' into branch-0.9-streaming-docs
d792351 [Chen Chao] maintain arbitrary state data for each key
e708f74 [Aaron Kimball] SPARK-1173. (#2) Fix typo in Java streaming example.
156bcd7 [Aaron Kimball] SPARK-1173. Improve scala streaming docs.
8849a96 [Andrew Or] Fix typos in Spark Streaming programming guide
fbd66a5 [Chen Chao] Merge pull request #579 from CrazyJvm/patch-1.