count should be reset to 0 on program load
Adding tests for unnext
removing _c from next and unnext methods
Simplifying tokeniser

removing difference between symbols and names, now just has names
Adding tests for tokeniser
tokens can now be passed to parser as construction args
Standardising method names a bit
Adding better error handling

Interpreter can now be given an error callback that gets given an error
message and the stack info when an error occurs
Interpreter now correctly keeps callstack
Runner now uses error callback
Adding error test script