Implements an REPL that can execute Morley instructions. REPL starts with an empty stack. At each instruction entered, the modified stack, or an error is printed. Multiple instructions separated by semicolons should work as expected. Available meta commads are:

':help', displays this helpn ':stack', prints the current stack ':loadstack filename', loads the stack from a file ':dumpstack filename', dumps the stack to a file ':clear', clears the current stack. Ctrl-D or ':quit' to end REPL."