Configure Travis CI matrix build
Configure Travis CI matrix build

The following environments are used:

* Ubuntu Precise (only cli tests are run)
* Ubuntu Trusty (cli and python tests)
* Mac OS X 10.11 / Xcode 7.3 / mozjpeg (cli and python tests)

lovell/libvips,lovell/libvips,jcupitt/libvips,lovell/libvips,jcupitt/libvips,jcupitt/libvips,lovell/libvips,jcupitt/libvips