DOC: closes gh6838. Breakout options.rst from basics.rst

closes #6838. 
closes #3104 
Breakout "options" section for docs, heavily using info already in ``basics.rst``. Expands examples, and turns ``describe_options`` into a table.
Updated for 1) .  For 2) I've re-titled and added a sentence.  I think it's important to delineate that this is not done through ``set_options``.