Added doc which describes how to contribute to fplutil.

Tested:
Built HTML docs and verified links work.

Change-Id: I6e7fe72d1236842e8d5eefa41bc953c2bdf8996b
Added support for searching prebuilts directory for projects.

Tested:
Performed a dry run push of a new project.

Bug: 18226263
Change-Id: I4a255c25088eb98b004715dd4725449cd0e065e8
Merge "Added support for searching prebuilts directory for projects." into ub-games-master
Added option to specify a revision to sync submodules to.

Tested:
Pushed a new project to github with these references.
Bug: 18226263

Change-Id: Ib2932797cc7535432c6eaf1351c098f254215d2a