Merge pull request #1 from bvssvni/master

Added Rust-Empty
Initial commit
Merge pull request #3 from PistonDevelopers/ccgn_image_formats

Initial commit
Rearrange src files
Merge pull request #4 from ccgn/master

Rearrange src files
Initial implementation of the ImageDecoder trait
Merge pull request #6 from ccgn/master

Initial implementation of the ImageDecoder trait
Convert PNGDecoder to use the ImageDecoder trait
Implement the ImageDecoder trait for all Decoders
Merge pull request #7 from ccgn/master

Implement ImageDecoder for all Decoders
add documentation
Merge pull request #8 from ccgn/master

add documentation
Upgraded Rust-Empty

Closes https://github.com/PistonDevelopers/rust-image/issues/9
Closes https://github.com/PistonDevelopers/rust-image/issues/10