Merge pull request #164 from nwin/master

Initial support for interlaced PNG images
Merge pull request #166 from nwin/master

Improve docs, mention possible panics.
Merge pull request #167 from nwin/master

Fixed palette interlaced images.
Update CHANGES.md
Ability to alpha-blend pixels, plus overlay separate images to produce a
new image
Merge pull request #168 from AngryLawyer/master

Draw image rectangles into each other, with alpha blending
Update Cargo.toml

Revert to git deps until rust stabilizes more. Fixes #169.
Fix pngsignature slice; change deprecated unwraps to into_inner
Merge pull request #171 from jameson-ernst/master

Fix pngsignature slice; change deprecated unwraps to into_inner
add benchmark
update to latest rust
Merge commit 'cd87733f9f232ea2ffd98bede995e10369391fa8'

Conflicts:
	src/png/decoder.rs