Sketch of includer, very borked right now.
Enabled extending the includer.
Implemented includer that does more than simple copying.
Added working writer.

Makes use of the builder and the new includer.

The builder could use a bit more work to function nicely with
this new method of writing.
Removed print line.
Actually removed the print line.
Removed a few unneeded lines.
Made the includer able to manipulate the included files.
Added includer to plugin.register function.
Removed commented out code.
Cleaned the builder a little.
Moved slugging into the GroupKey class.
Bumped version.
Merge pull request #15 from cknv/includer

Includer
Added shorthand imports.
Added classmethods and new register function.
Bumped version.
Removed old plugin code.
Tweaked the writer for better external iteration.
Forgot to actually calling the files function.