Provide cleaner way to generate documentation

This allows the documentation to be generated using a Makefile, with
defined but configurable locations for output.

This also allows the version to be injected into the output as well, so
that it can reflect the latest source version

Change-Id: Iebfde5d674b7da60f7cf899d925e38773e8a2e32
Reviewed-on: http://review.couchbase.org/39315
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>