fix typos

Remove the rest of internal module coupling between packages

minor doc changes

optimize texture property access to bypass the getter

fix rendering problems with mesh and rope

Fix Mesh Rendering to enable pixi-spine Mesh to render properly

fixed extends doc issue

update indices data before drawing

Move items into their namespace ...

This commit also:

 - fixes some dangling whitespace,
 - fixes some incorrect docs in extras/mesh,
 - moves Text to core
 - moves BitmapText to extras
 - moves math constants to const.js

Fix all the remaining jshint stuff

Moved the mesh folder to the root