Logstage: macro helper for logging method calls with parameters and returns

```scala
log.logMethod(Debug) {
  f(a, b, c)
} // call to f with a=1 b=2 c=3 produced res=6
```

```scala
(f(-1, 2, 3): F[String, Int])
  .logMethod(Debug) // call to f with a=-1 b=2 c=3 produced error="Number must not be negative"
```