fix clang errors

[ludflu]

• fix problems with casting unsigned ints to (void *) pointers
• these changes allow us to compile PortMidi for OSX again.

[OlivierSohn]

LGTM, there are lots of formatting changes but the code seems more readable now.

[dpwiz]

Is it possible to split commits into formatting and then actual fixing?

[ludflu]

yes, i'd be happy to do that

[ludflu]

Is there anything else I can do to help move this along?

[OlivierSohn]

I am not familiar with this code at all, but after looking at how the descriptor field is used in the code base, the changes seem to be reasonable.

I think I would prefer if the macro for casting is removed and casts are in the code directly.

@dpwiz are you more familiar with this code base, what do you think?

[dpwiz]

There were a few more warnings about pointers, so... #22