Refactor with grasp

Instead of using string replacement we're using Graspjs.
Enable `export var foo` by extending `this`

Originally `this` was never touched by local variables behind `export var foo`,
but a bit of Grasp and some Underscore and it's working perfectly.
Add a Travis CI configuration file
Remove Grasp wrapper dependency

With the new version of Grasp, you don't need to have a wrapper – you can just
call it with Grasp.replace().
Merge branch 'master' into add-grasp

Conflicts:
	package.js
	plugin/compile-harmony.js