make bc_eval use OWHILE instead of WHILE
move next_addr overload to bytecodeTerminationScript.sml

so it's more easily accessible by the implementation
initial repl implementation

Define a function repl_fun : string -> repl_result.

Caveats:
 - cheating on definition of parse
 - cheating on definition of print
 - does not handle exceptions
 - does not handle modules
 - no proofs about it