`logf` should support interpolated strings

[jwosty]

The following should work:

let durationMs = 5. / 3.
logfi ml $"Duration: %.2f{durationMs}ms"

Currently, this blows up with a runtime exception.

IIRC, this might actually be impossible to implement at the moment. Will investigate again to verify.

[jwosty]

Blocked by: https://github.com/vbfox/MasterOfFoo/pull/5