For Travis CI - misc. minor fixes.
- Fix commit message when performing API documentation update.
- Use single process when packaging to prevent make process being killed due to out of memory.
- Use one less process when building samples for MinGW/64-bit/STATIC target due to out of memory.
- Use commit-ish to describe the version number when renaming source package.
For Travis CI - switch CI build to use OS X build environment.