upgrade the spine support to both latest version of the Spine framework and melonJS

[obiot]

The current version of the melonJS spine plugin (https://github.com/melonjs/melonjs-spine) is based on melonJS 2.0 and Spine 1.1 !

A new version of the plugin would be :

• based on the latest ES6 version of melonJS (version 13.x a the time of writing this)
• based on the latest 4.x Spine Runtime
• be available as an independent es6 module (that can be transpiled for example when added to our [boilerplate])(https://github.com/melonjs/es6-boilerplate)
• provide a fully working example
• provide at least a minimal implementation (extra features such as wireframe and others is just nice to have but not mandatory)
• The implementation shall provide a "SpineObject" (name is an example) that extends the melonJS base Renderable object, which already provide all the necessary "tools" (transformation matrix to be applied, blend modes, etc...
• Only rely on melonJS Renderer class (as opposed to directly call Canvas or WebGL function) to abstract from the final canvas or WebGL rendering/drawing mode