more specific compiler errors, more general make_guard!

[sarah-quinones]

amazing crate! hope it's fine for me to suggest a few improvements

this pr makes the constructors of Id and Guard const, allows multiple identifiers in make_guard!, and makes the compiler error for mismatching lifetimes point to the relevant guards instead of the compiler always complaining about branded_place, which should be an implementation detail

[ArhanChaudhary]

@CAD97 you should take a look!

[CAD97]

Current compilers don't mention branded_place by name anymore, so I'm going to go ahead and close this for now. Rust also doesn't really do multiple declarations in one line, so I don't really think that doing so for make_guard! is really necessary. While creating multiple branded lifetimes is useful for showing the compiler error, it's very rarely needed in brand-using code anyway.

[ArhanChaudhary]

Oh right, I didn't even realize temporaries weren't called out by name any more. What about the #[inline] stuff for this PR? That looks useful.

[CAD97]

There was a change in the compiler at some point that "trivial" functions in MIR are automatically given equivalent to #[inline] treatment. They all get inlined at the MIR level already, so there's no need to further press on the compiler and mess with the heuristic differences that exist between debug and release, imo.