make all configuration configurable

As a user
I want to be able to change all sprocket settings
In order to adjust them to my projects needs
add tests
Update asset_pipeline_spec.rb
Merge branch 'patch-1' of github.com:nesQuick/sinatra-asset-pipeline into nesQuick-patch-1

Conflicts:
	lib/sinatra/asset_pipeline.rb
	spec/asset_pipeline_spec.rb