Improve REPL
Improve REPL

Not fully functional yet, but it does featurei

* rolls back when your commands do not compile
* prints error messages
* actually compiles now (because `go run $FILE` requires $FILE to end in '.go')

If this printed out the output from the run command, I'd be a pretty happy camper

tjarratt/go-experiments,tjarratt/go-experiments