Install script

[ear7h]

This PR contains an install script which builds Mapbox.framerwork and a few library (.a) files and places them in appropriate locations for building go-mbgl.

Notes:

• sudo is required to place the .framework in /Library/Frameworks, the build would fail otherwise even with -F switch
• it will install mason-js globally
• tests now occasionally fail on exit
  • possibly due to the cache file generated by DefaultFileSource

[ARolek]

The script worked for me. Thanks for putting it together.