Merge pull request #125 from bvssvni/master

Merge expression branch into master
Merge pull request #126 from bvssvni/master

Removed adventure example
Merge pull request #128 from bvssvni/master

Moved stuff over from piston
Merge pull request #129 from bvssvni/master

Fixed example
Merge pull request #131 from bvssvni/master

Added more docs
Updated README
Added link to online docs
Deriving `PartialEq` for `Behavior`, `State` and `Status`
Added states back

Closes https://github.com/PistonDevelopers/rust-event/issues/132