Change doc build process to pull in docs from all the falcor projects

[ktrott]

In API Reference navigation on the main Falcor site, we would represent each Falcor project separately as sub-nav item.

[steveorsomethin]

Some notes:

We still want this. Each project should build its own docs. Main site should link to individual doc sites. Docs should build as part of release process rather than per checkin.