✨ fn_abi

A proc attribute macro that sets the ABI/calling convention for the attributed function.

Example

```rust

[macrouse] extern crate fnabi;

[abi("fastcall")]

extern fn helloworldfastcall() { println!("hello world!"); }

[cfgattr(all(targetos = "windows", targetpointerwidth = "32"), abi("thiscall"))]

[cfgattr(all(targetos = "windows", targetpointerwidth = "64"), abi("fastcall"))]

extern fn helloworldwindows() { println!("hello world!"); } ```