Fixed trailing slashes for xml font files' images (#2680)

Fixes loading bitmap fonts from data URIs (both FNT and Image)

fixed kerning undefined error

Changes for pixi-compressed-textures ...

1) newer version of resource-loader
2) pass the metadata to images
3) export WebGLManager

Depecrate `PIXI.math` namespace ...

Access math members from PIXI when outside of core, require the math module directly when inside of core.

Remove the rest of internal module coupling between packages

less ducktyping, use is* from loader; fixes #1628

Merge remote-tracking branch 'origin/dev' into dev

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