src/itx.rs: Deduplicate w/ generics

[thedataking]

First commit emits debug info for assembly on debug builds. This aids testing and debugging. Closes #25.

NOTE to self: need to update the macro docs in bitdepths.rs if the overall approach looks good.

[kkysen]

I haven't thoroughly reviewed the macros and initialization logic (comparing them to C), as you said you looked at that pretty thoroughly already. I can if you think you could've missed something, though. Besides that, I had a few other small comments. Also, the debug info improvements are very nice.

[randomPoison]

The translation of the C macros looks correct to me. Is there a reason you didn't setup macros for assigning the C fallback functions though? I'm assuming it's correct because what we should have should be the direct result of expanding the macros in C and should have been the same between the 8bpc and 16bpc files, so if you copied it out from one of them then it should be correct here. But it's hard to verify without having the macros setup the same way.

[kkysen]

We can later change the fallbacks to return Self, which will check that we initializedeverything. So I'm less worried about them vs the asm ones.

[thedataking]

Is there a reason you didn't setup macros for assigning the C fallback functions though?

Derp, I forgot to push that change; sorry about that .

[randomPoison]

Updated macros for initializing the fallback fns look good too 👍 Thanks for adding those.