[SPARK-5166][SPARK-5247][SPARK-5258][SQL] API Cleanup / Documentation
Author: Michael Armbrust
Closes #4642 from marmbrus/docs and squashes the following commits:
d291c34 [Michael Armbrust] python tests
9be66e3 [Michael Armbrust] comments
d56afc2 [Michael Armbrust] fix style
f004747 [Michael Ar
[SPARK-5166][SPARK-5247][SPARK-5258][SQL] API Cleanup / Documentation
Author: Michael Armbrust
Closes #4642 from marmbrus/docs and squashes the following commits:
d291c34 [Michael Armbrust] python tests
9be66e3 [Michael Armbrust] comments
d56afc2 [Michael Armbrust] fix style
f004747 [Michael Ar