Updated explanation of Holland, added section

Updated the explanation of Holland in the intro section and also added
a (currently incomplete) Installation section.
Updated parts of the docs to use provider-plugin

Various parts of the documentation now refers to providers as
provider plugins. Also made minor grammatical updates.
Started work on refactoring the provider configs
Expanded on provider plugins, added examples
All parameters now use .. describe:: in config.rst
Lightly exapnded on plugin explanation
Deprecated plugins_dirs in docs for 1.0.8+
Fixed Typos
Formatting for version and deprecated tags
Merge pull request #93 from m00dawg/master

Documentation Changes