Resize the shape in Tiled instead of manually resizing
Create polygone based shape by default instead of rectangle
Added polygon (SAT) collision code

Not yet used, as the me.PolyShape object still misses some bits in order
to work (like `normal` points, that are calculated through the `recalc`
function in SAT.js)
added the "missing" recalc function to me.PolyShape, that calculates the collision polygons

Note : the current polyshape implementation lack offset and angle
management, and is therefore more simple than the one in the SAT.js
library (this can be added later once collision is properly working)
added and enabled polygon to polygon collision testing!

also removed the now useless testRectangleRectangle function.

Collision response is not yet properly taken in account, and the x.y
value for backward compatibility are bit off for now, will fix that
later !

Also, still some cleaning to do in the code ;)
Fixed the x/y property values in the collision response object

it’s fully working now !!!
Merge branch 'polygonToPolygon'