Document file!() and line!() macros

[orenbenkiki]

** ORIGINAL ISSUE **

Title: Provide macros similar to CPP's __FILE__ and __LINE__.

Perhaps file!() and line!()?

[alexcrichton]

These actually both already exist :)

$ cat asdf.rs
fn main() {
    printfln!("%? %?", file!(), line!());
}
$ rust run asdf.rs
warning: no debug symbols in executable (-arch x86_64)
"asdf.rs" 2

[orenbenkiki]

In that case, they should be listed in the documentation...

[alexcrichton]

That is a good point, reopening and tweaking title, original was

Provide macros similar to CPP's `__FILE__` and `__LINE__`.

[alexcrichton]

Actually, closing as a dupe of #6444