GSoC: dinput8 Action Mapping

[Lucas Zawacki]

> Because callback doesn't have any string parameters it would be an easy
> thing to do.

I've made an EnumDevicesBySemantics version using A -> W calls, but it
turned out to be trickier than I thought because the callback function
is passed the device interfaces and then the A callback gets W
interfaces. I'll send the patches with corrections later today but I
really think the implementation for EnumDevicesBySemantics should
remain separate right now.