TravisCI

Here is a minimal TravisCI config, that will just compile haxe, haxelib and haxedoc.
It is working correctly on my branch, as shown at https://travis-ci.org/andyli/haxe/builds/11734295
I would like to let it run the unittests too, but there will be some modification on the test runner, so I will leave them to the later pull requests.

Before merging this pull request, please activate TravisCI first:
 1. Head to https://travis-ci.org/profile
 2. Select HaxeFoundation from the left hand side
 3. Switch this repo on.