[#164] Prevent TypeError with invalid `me.game.remove(null)`
[#196] Allow `alpha` and `volume` to be set to 0.

- Bonus: Fixed an error message!
ticket #196 : use explicit type check when checking the given parameter
use a regexp when checking for MSIE
Update me.Vector2d methods to return a reference to `this` for method chaining.

Example:
var vec = new me.Vector2d(
    Math.cos(Math.PI / 4),
    Math.sin(Math.PI / 4)
).scale(new me.Vector2d(16, 16)).floorSelf().negateSelf();

- Creates a new unit vector at 45 degrees.
- Scales the vector to 16 units.
- Floors the product.
- Negates the result.
Update collision_test example to use full playfield.

- A gap around the screen edges was introduced when the entity size was changed.
also unload atlas resources when calling `unloading()`
[#195] allows changing the imageLayer default origin point using the anchorPoint
[#195] fixed position calculation to match with "renderable within entity"  implementation

Default anchor point is however `(0,0)` to match with Tiled
implementation, while default anchor point for renderable is `(0.5,
0.5)`
[#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
Prevent multiple Tweens with successive calls to me.game.viewport.shake()
[#167] small README update
small fixes