Added in manual blending modes.
Made jslint happy.
Removed progress references.
Fixed aligning images when blending with different dimensions.
Put blending modes in a nested scope.
Simplified blending code.
Renamed r1, g1, b, … variables.

Variables now start with s or d (source or destination pixel) or o (output pixel).
Removed unused parameters.
When opacity is set to zero, make sure it's not set to 1 by mistake.
Renamed amount variable to opacity to better reflect its purpose.
Fixed calculation of the area that should have pixels composited.
Merge branch 'blendmodes' into blendmodes5

Conflicts:
	img.js
Fixed: canvas examples now also load blend.js
SVG Blending modes.