[#167] use grunt for the build system

first pass update (time for lunch!) and currently broken.
(based on the grunt_config file initially provided by bsparks)
[#167] upgraded to grunt 0.4 and fixed the build system

Currently broken (todo) :
* jshint : generates too much error and is not part for now of the
default build option (source code need lots of fixes first)
* coffeescript : requires a new .coffeescript file (can anyone help?)
* banner: removed from now as format changed with grunt 0.4
* jsdoc; to be added (together with a new template for version 3.x)
[#167} removed the now useless version.js file (version is now defined in package.json)
[#167] some attempts with jsdoc

this is not working for now as it seems there is some issue while
fetching jsdoc from the repository (npm issue?)

temporary fix `npm install` by removing `"grunt-jsdoc": "~0.3.2"` from
`package.json`
[#167] created a local task for jsdoc3

* doc generation is currently broken due to wrong comments format in the
melonJS source code
* template is to be updated as well
[#167] changed keyword to `doc` for jsdoc generation
[#167] updated the build process in the README file

need for sure some further update :)
[#167] added coffeescript dependency

a specific Gruntfile.coffee is actually required for it