Input module ergonomics and features

[AlisCode]

Hey there!

Currently, the input module of ggez-goodies does not :

• Implement default for InputState (which makes it impractical to work with e.g. Specs, and also violates the Rust API Guidelines on common traits),
• Support Gamepad (in InputBinding), even though ggez itself does,
• Support multiple players
• Support mouse (even though I dont care for my use case)
• Have an example on how to use it (even though it's fairly trivial by reading the docs)

I will have a PR on its way this weekend. I'm posting this issue to see if the project is still active (since latest commit on devel branch was 6 months ago ?)

[icefoxen]

Heck, feel free to just input entirely if you need to. This project is maintained entirely on a "when I need to and can get around to it" basis, unfortunately, and cleaning up input has been on my to-do list for a long time.