Add a script to build an HHVM RepoAuthoritative bytecode file

Add a script to build an HHVM RepoAuthoritative bytecode file

This script compiles a list of known MW sources, including core and
extensions, and generates a RepoAuthoritative bytecode file. Some ideas
were taken from Bryan Davis's scap-hhvm-compile shell script.

Also, renamed the old maintenance/hiphop directory to maintenance/hhvm,
respecting the rename of the upstream project.

Change-Id: I55798729d0553d2840e8099e81d604a814e8664c