AssetType specifies all the different formats, rename to AssetFormat.

This was necessary since saying something like:

    // Crazy php script that generates an MP3
    manifest.add("foo.php", Audio);

wasn't precise enough to figure out if the browser should load it (it
could be an unsupported audio format). Now that should be:

    manifest.add("foo.php", MP3);

Fixes #98.
Fix blob responseType detection in IE.
Merge branch 'master' into haxe3

* master:
  Fix blob responseType detection in IE.
  AssetType specifies all the different formats, rename to AssetFormat.

Conflicts:
	src/flambe/platform/html/HtmlAssetPackLoader.hx
Added Mask blend mode
Changed HtmlExternal to bind functions to the container

This is more consistent with the way it works for Flash, and
also allows works when using multiple Flambe instances.
flambe.embed can take a callback that is fired when embedding is complete
CanvasGraphics#clear now uses clearRect instead of fillRect

Using fillRect could break transparency.
Initially add canvas with no width/height

This is because some browsers (e.g. chrome) give a default width/height
that can cause it to become larger than its parent, breaking stage size
detection.
Fix some issues when using with haxe 3 rc
Initial changes to support a shared context in flash mode
Don't alter the stage when using a shared context
Initial changes to support a shared context in HTML mode

At the moment the shared flag has no effect, but a context can be passed in.
Fix initialising a Flash stage when no context is given
Added a method to Texture to get the bounds of an area matching a color

Behaves similarly to BitmapData#getColorBoundsRect
(http://help.adobe.com/en_US/as2/reference/flashlite/WS5F7E996C-A0F6-4d89-BC17-69622D209F21.html).