Port of impersonator gem

Now that there are some VCR ports available ([vcr.cr](https://github.com/spoved/vcr.cr), [hi8.cr](https://github.com/vonKingsley/hi8.cr), [eighttrack](https://github.com/russ/eighttrack)) it would be nice to have something like [impersonator](https://github.com/jorgemanrubia/impersonator) as well.