Added a json map to play with :)
fixed json loading and first parsing (from responseText)

although the basic tmx parser has been modified, the final approach I
choose is to create a new map reader object, that will allow to remove
the data format stuff from the map object (as the map reader object will
populate the map, as in Tiled), and then ease implementing a specific
json parser.
First pass refactoring
Further update : definitely not a quite walk in the park
Added basic JSON support for map properties and tilesets

ImageLayer, Layer, ObjectGroup and Objects still to be done !
Added JSON parsing for ImageLayer
Added JSON parsing for TileLayer

One to go ! but time to sleep first :)
added JSON parsing for TSX (UNTESTED)
added JSON parsing for ObjectGroups/Objects

remaining issues :
* tile collision is currently broken
* alpha settings are not applied
* polygone, polyline objects is broken
Fixed tileset gid value when setting tile properties
Fixed an issue where int value are set as String in the JSON map
Fixed values passed to the renderable component

JSON seems to export user-defined properties as String (even for Integer
based values)
Fixed various parsed value types
Fixed json parsing when applying properties
Fixed the "double entity" bug :)
Move the Tiled Layer data parsing out of the layer object (avoid duplicating dead code once initialized)
Merge pull request #168 from obiot/ticket-140

Ticket #140 : support JSON map formats