Merge pull request #463 from TyOverby/partialfix

automatically derive PartialOrd for Key
Add .travis.yml
Merge pull request #465 from TyOverby/travis

Add travis configuration
Added Travis build status indicator.
More detailed Travis status indicator.
Activate Travis build

Closes https://github.com/PistonDevelopers/piston/issues/466
Removed part about documentation

Closes https://github.com/PistonDevelopers/piston/issues/468
Added link to Piston-Examples

Closes https://github.com/PistonDevelopers/piston/issues/469
implement Ord, PartialOrd, Eq, PartialEq by hand