parser.py: Implementing expression method
parser.py: Implementing expression prime method
parser.py: Implementing term method
parser.py: Fixing comparison of tokens in expression prime method
parser.py: Implementing multiplication grammar for term prime method
parser.py: Implementing entire expression prime grammar method
parser.py: Implementing entire term prime grammar method
parser.py: Implementing factor grammar
parser.py: Implementing goal grammar method
parser.py: First pass at implementing expressions parser
parser.py: Parser can now parse a + b * c