Keyboard support

[a60915]

We are using this library to allow users to select a state and need them to be able to do this using the keyboard. I have it working with most of the changes currently in our solution, but it's relying on how the internals of us-map works and I made one change to alphabetize the past list. Is this something that others would be interested in? If so, I could migrate my changes into the library and submit a pull request.