Comparison with established keyboard libraries

Hi Keith,

How does this library compare with established/more popular keyboard handling libraries like [MouseTrap](https://github.com/ccampbell/mousetrap), [keymaster](https://github.com/madrobby/keymaster/issues/139) and [Keypress](https://github.com/dmauro/Keypress/)?

Can you add a little to the README advising the user to choose among these?
