added test + updated documentation

Some tips and a test to show only the provided extension-files are
being processed/generated.
Merge pull request #1 from jeroenvanmaanen/master

Smarter use of .files inside this plugin.
updated "extends" functionality due to merge

added multiple options/features, but had to update code to make it work.
v0.5.0

updated docs and published
updated documentation + fixed faulty input
v0.6.0

"extends" as an option and not default, which forced a rewrite of some
features/options.
updated documentation

some textual fixes.
updated documentation
Register only those helpers and partials that are declared in the context.
Merge.