Update Grunt to v4.0
Update vendor files
Replace grunt.util.async with async module

grunt.util.async is deprecated.
Fix the path of CoffeeScript compiler

See http://coffeescript.org/#changelog for details
Fix coding styles according to JSHint

trailing whitespaces, unused variable declarations, and missing
semicolons
Add license statement falafel

falafel is licensed under the MIT license
Ignore temporary directory