Multiple Directory Support

This adds support for passing an array of paths as `src` that will be sequentially tested for a source file, and ultimately return 404 if no matching file is found.  The first match will be the rendered match.

This is implemented as a branch from `0.1.15`, as this starting point seemed a bit more straightforward – I'm opening the pull request to `master` as I'd like to have support for this in the updated version, and am willing to change the implementation to do so.