Command-line interpreters for lexer and parser

[adamjstewart]

For demonstration purposes, it would be nice to have command-line interpreters for the lexer and parser so we can interactively demo them.

[ZaidQureshi]

Yes, be my guest to make it. It should be very similar to the already existing interpreter, except for the fact that instead of calling eval_dec you print the input. Or you can even print this in the current interpretor.