Start some pretty-printing (taken from website).
Restructure, into a main driver and an ast file.

The ast defines an abstract syntax tree, as well as
functions to evaluate and string-ize an ast.

The driver, currently, just creates a dummy ast
and tests the printing and evaluation of it.
Setup basic structure.

Create lexer and parser modules, and have main
read from stdin and call the lexer and parser.

Currenlty, these just return dummy values
(the same as in the previous commit).
Implement hand-written recursive decent parsing.

This involved a re-writing of the ast.

Works (including the proper association for - and /).
Change ignore file to ignore executable name