Move Window.get_size into implementations

Depending on the default trait implementation was insufficient as the trait used the size the window was constructed with, which is wrong if the window has ever changed size.
Merge pull request #144 from jakerr/get-size

Move Window.get_size into implementations
Renamed `Not` to `Fail`

Closes https://github.com/PistonDevelopers/event/issues/130
Merge pull request #145 from bvssvni/master

Renamed `Not` to `Fail`
Fixed comments
Merge pull request #146 from bvssvni/master

Fixed comments
Fixed comment
Merge pull request #147 from bvssvni/master

Fixed comment
Added WhenAny behavior

* Fixed bug in WhenAll

Closes https://github.com/PistonDevelopers/event/issues/142
Merge pull request #148 from bvssvni/master

Added WhenAny behavior
Use same algorithm for `Select` and `Sequence`

Closes https://github.com/PistonDevelopers/event/issues/149
Merge pull request #150 from bvssvni/master

Use same algorithm for `Select` and `Sequence`
Added After behavior

Closes https://github.com/PistonDevelopers/event/issues/120
Merge pull request #152 from bvssvni/master

Added After behavior
Updated title in README
Removed optional methods on Window

Closes https://github.com/PistonDevelopers/event/issues/157
Merge pull request #158 from bvssvni/master

Removed optional methods on Window
Added GenericEvent

Closes https://github.com/PistonDevelopers/event/issues/159
Merge pull request #161 from bvssvni/master

Added GenericEvent
Added EventTrait

Closes https://github.com/PistonDevelopers/event/issues/160