Add mouse-movement events

[idupree]

Currently you can synthesize mouse-clicks in the same way as if a mouse-button were a key (as of #7 ; an example code name is key.CODE_BTN_LEFT).

We would like be able to create mouse movement too. This is example C code using uinput to move the mouse:
http://git.nosuchfile.org/?p=uinput-sample.git;a=blob_plain;f=uinput-sample.c;hb=HEAD
as linked on
http://thiemonge.org/getting-started-with-uinput

I don't have quite a good enough sense of the gostwriter code organization yet. Where do you think is the best way to add another uinput event type? For event types, we currently have EV_KEY and mouse-movement would be EV_REL.