Mark "bored" specs as pending for now
implement two-operand addition
Support n-operand addition
Subtraction
Multiplication
Division
re-enable the first evaluate spec
horrible tokenization/evaluation thing
add spec for multiple add/subtract (technically a freebie, since it passes)
Re-enable the next spec
ignore whitespace
Extract Tokenizer
Encapsulate list of tokens
Rename 'tokenizer' to 'tokens'
Make comments unnecessary by making Tokenizer's API more expressive
Extract Evaluator class
Move local variables to private accessors
extract method for processing operator
extract method for processing integer
oh, look, that didn't need to be anything but a local