Allow texture to not be flipped

jslinted code

Docs updated ...

Fixed issue where alpha not being set correctly in canvas spriteBatch
Fixed issue where previous stage events did not get removed correctly

Typos and Started tackling the WebGL, and tests

Docs :)

Fixed, finally adapted to the dev branch

Manually merge #522 from @qzix13

Added auto prevent default variable to pixi constants

Mad cross origin on by default to fix ie11 issue and make life generally easier

Added constant for interaction frequency

Fixed premultiplied alpha - for webGL transparent canvas

Added clear rect to transparent canvas renderer

Jshinted code

Finished first pass of webGL destroy functions

Fixed render texture issue where textures not getting uploaded to GPU before render

Jshinted code ...

also tweaked BaseTexture.fromCanvas function

Added fromCanvas to base texture ...

added destroy function to webGLRenderer (WIP)

Implemented texture caching for fromCanvas method

update scale modes constants

Forgot to update that one!

Fix texture scaling in canvas renderer

Tweaked mouse up interaction to work inline with expectations ...

commented out unused {}

Fixed hoever interaciton inconsistency ...

Also changed canvas renderer to use fillRect instead of clearRect as
its faster and works with the new alpha property that canvas has

Fixed scale Issue with text

Fixed bug in canvas when using masking and blend modes ...

Also removed canvas alpha property temporarily as the new feature needs
to be full tested

Fixed issue with transparent webGL renderer in FF

Moved Constants to pixi.js file

Added alpha:transparency to canvas renderer

Fixed rollover issue with mouse

updated the visible check for display objects