Uncomment start call

Not that there are some tests in place, and we're ready to start
the tutorial, enable the start method.
Try an alternative to killing the process for aborting.

Killing the process isn't very good for repl testing etc.  Also
since everything is run in a class its not really necessary to kill
the process.
First implementation of expression

Just reads a single number.
Expression: Addop implementation

Implementation of expression that reads single digit numbers and
optional add (+) and subtract (-) operations between two single
valued integers.
Expression: Addop Implementation improved

*Add ability to have more than a single Addop
*Add comments to assembly output
Expression: Addop Implementation Bug-fix

Fix bug where result of add/subtract was left in EBX, but expression
is expecting the result of the computation to be in EAX and hence
pushes it to the stack before reading the next Addop.
Fix Halting condition

Remove the go flag since its not being used.  The compiler halts after
it stops matching.
Expression: Mulop Implementation improved

*Add ability to have multiply and divide operations
*Fix assembly output so that add, sub, mul and div use the same pattern
 for storing and retrieving arguments from stack during computations.
Expression: Mulop Implementation improved to allow parenthesis

Add ability to use parenthesis in expressions to group sub expressions.
Expression: Mulop Implementation improved to allow negative factors

Crude implementation to allow factors to be negative by translating
them to 0-X or 0+X expressions.