Added maintainers to README

Closes https://github.com/PistonDevelopers/image/issues/122
Fail example if necessary.
Fixes #133
Refined comment.
Fix deprecation warnings.
Merge pull request #135 from nwin/master

Fix for #133
Merge pull request #136 from nwin/master

Fix deprecation warnings.
Upgraded to latest Rust

Closes https://github.com/PistonDevelopers/image/issues/137

* Added Primitive placeholder trait
* Added `max_value` to replace deprecated Bounded
* Added imports to Float, SignedInt and FloatMath
* Removed Num constraint on clamp functions
Merge pull request #141 from bvssvni/master

Upgraded to latest Rust
Always read the background field.
Merge pull request #143 from nwin/master

Fix possible bug in gif.
Make color::Primitive trait public
Merge pull request #144 from tomaka/master

Make color::Primitive trait public
Added link to how to contribute

See PistonDevelopers/piston#715
Removed some spaces

Closes #140
Merge pull request #146 from leonkunert/master

Removed some spaces
Fix for change to enum namespaces
Merge pull request #148 from gchp/enum-namespace

Fix for change to enum namespaces
Update .travis.yml

Disable automatic tests for now. As long rust has so many breaking changes they are not very helpful.
Change occurances of rust-image to image