An attribute macro that logs the return value from function call.
This is a reimplementation of the log-derive
crate with async-trait
compatibility.
```rust use logcall::logcall;
fn foo(a: usize) -> usize { a + 1 }
fn main() { envlogger::builder().filterlevel(log::LevelFilter::Info).init(); foo(1); }
// prints: // [2023-07-21T12:57:43Z INFO main] foo() => 2 ```