Add some functions, fix some stuff

[lunabunn]

• BOOL should be a typedef for c_int
• PFD_TYPE_RGBA, PFG_TYPE_COLORINDEX, PFD_MAIN_PLANE, PFD_OVERLAY_PLANE, and PFD_UNDERLAY_PLANE should be BYTE
• c_struct! should generate structs with public fields
• Add the following functions:
  • GetProcAddress
  • DescribePixelFormat
• Add the following types:
  • FARPROC
  • NEARPROC

[lunabunn]

There are a lot of other constant types that are wrong, but 🤷

As per #2, is the convention meant to be that consts are left as u32 and the user casts them as appropriate? Not sure why this would be preferred over just having consts be the correct type. Or did I just misinterpret the issue?

[Lokathor]

There's places where the C api isn't even consistent about what type a value is supposed to be, is the problem.

I can accept the new types and externs, but the changes to types are a breaking change technically.

If there is gonna be a 2.0 we should go farther and use more actual newtyping and repr(transparent) stuff. Like the newer style in the windows-rs crate.

[lunabunn]

Ah, right, those would be a breaking changes. In the meantime, I guess we are stuck with casting constants as necessary? (Or taking the module approach, as described in #2)

[lunabunn]

The pub fields thing is technically also a breaking change, though, (AFAICT) and that's just broken w/o a workaround. Can that be merged, at least?

[Lokathor]

making the fields pub is allowed, you just can't make them private again after that. And if all fields are pub and then structure isn't non_exhaustive you can't add more fields (pub or priv).

But going from some amount of private to all public is legal.

[lunabunn]

Ah, right, I'm only making private fields public not adding new fields. Got confused there.
With that out of the way, I rolled back the breaking changes, should be ready to merge.