Rework the augeas state/module

Corrected some style faux-pas in the state, and made the arguments more
"salty" by making them key-value pairs, rather than space delimited
value pairs. Also corrected invalid "changes" return data.

In the module, made some of the logic more Pythonic, as well as raising
exceptions when invalid arguments are specified.
docs update: add augeas state to toctree
Merge pull request #7109 from terminalmage/issue6994

rework the augeas state/module