fix some bugs in the loader

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 loading of bitmap font

get relative bitmap font loading properly.

better detection of bitmap font; should be relative to xml url now

loader already passes baseUrl, don't need to do it in add

Docs fixes, improved the consistency of the deprecation, thanks @englercj ...

Also added a comment on the bitmap font parser, will leave the change
until we find a new caching system

fixed typo in cacheAsBitmap, fixed bitmap text and restored the font cache so we can debug it

fix logic error in bitmapFontParser check:

bump resource-loader version and use add

update to latest loader

initial texture rotation support

add loaders and spine exports; fix typos in loader; add async dep

implement bitmapFont and spineAtlas parsers

implement bitmap font loader