Bootstrap scripts

Took the idea from Jekyll for a few easy scripts to setup the environment for a new dev.

 - `bootstrap`: sets up required clones below the project directory
 - `spec`: runs bootstrap and then the sass-spec tests with a temporary `SASS_LIBSASS_PATH` value
 - `branding`: prints the libsass ASCII art header
 - `cibuild`: most of the logic from the old travis.sh for conditionally running the automake + the new `spec` script