optimize texture property access to bypass the getter

fix rendering problems with mesh and rope

fixed extends doc issue

Rope supports textures from spritheet

fix const usages in plugins

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

render methods are private

minor doc cleanup

Moved the mesh folder to the root