Avoid missing python.exe target error reported in #71.
Doc: Note that Mercurial needs purge extension enabled.
Doc: Note that autoconf is required.
Add more high-level logging to build scripts.
Surpress most build output except for errors and warnings.
Doc: Note that automake is required.
Doc: Add notes on how to install build dependencies.
Travis: Pass xctool args manually, since we're invoking manually.
Travis: Ensure autoconf and automake are present.