Prepend URLs for all asset types (remote & stylesheet, as well as local).
Revert "Prepend URLs for all asset types (remote & stylesheet, as well as local)."

This reverts commit a799a83b64b2f29544eee840999df188fafe0629.
Correct prepending for remote & stylesheets.
Correctly define usage() as a static method (thanks @johanneslamers)
Version bump: 2.1.13