Fixed type error
Put `BackEnd` and `Observer` in separate files
Merge pull request #8 from Coeuvre/master

Put `BackEnd` and `Observer` in separate files
Added `remove_observer` to back-end
Merge branch 'master' of https://github.com/PistonDevelopers/rust-event
Merge pull request #12 from Coeuvre/master

Added `remove_observer` to back-end
Updated links to docs
Rename event context to follow the discussion of #10
Add missing files
Merge pull request #13 from Coeuvre/master

Rename event context to follow the discussion of #10
Added `AddRelease`
Added `ReleaseKeyboardEvent`
Merge pull request #14 from Coeuvre/master

Added `AddRelease` and `ReleaseKeyboardEvent`
Renamed 'Map' to 'Call'
Updated `README.md`
Merge pull request #19 from Coeuvre/master

Renamed 'Map' to 'Call'
Removed `BackEnd`, Added `EventCenter`
Merge branch 'master' of https://github.com/PistonDevelopers/rust-event
Merge pull request #22 from Coeuvre/master

Removed `BackEnd`, Added `EventCenter`
generic attempt