redirect to cleaner URLs without file extension or directory index
filename (index.html or README.md)
Fixes#732
Change-Id: I6332571b2d8ec1ea48e697d31017eb6a63fe1a12
don't strip the "/doc" prefix, which simplifies some of the file
handling logic. Also add a test case for the /docs/ => /doc/ redirect.
Change-Id: I96c60bc031daaeff7f78ca854b60bdc542913b3d