fix for move_rel and move_abs not working on Linux

[positiveway]

fix for issue #50

[positiveway]

@obv-mikhail can you please review this? I would like to contribute to this library by submitting fixes and features via PRs rather than making my own fork.

I have other PRs planning:

• Issue In Linux implementation some keys have the same codes as Numpad keys #52
• Implementing common Trait for KeybdKey and MouseButton. Quite useful in my case. I am mapping controller keys to keyboard and mouse ones. So storing layout (pairs) in HashMap seems like a logical option. Currently, mouse keys and keyboard keys can't be stored together although they provide the same methods. This one I already implemented locally.
• Currently bind_all overwrites previous bindings for specific keys. It would make sense to only use a common handler for keys that currently have no handler at all. Proper implementation of this unction would be adding a parameter rebind. If true all previous binding would be cleared.
  • Or an even better way - chained callbacks. First calling the common handler and then a specific handler for a key. Need to look into this more. Idea was already proposed in Support binding a key multiple times #10

It would be more convenient to submit PRs in subsequent order after a previous one has already been approved.

[obv-mikhail]

@positiveway looks good. Thanks for the PR.