Added accessor for Parser command.
Printing labels that are found.
Answers "Can I detect the labels easily?"
Extracting symbol from the parenthesized label.
Answers, "How can I get the parser to just give me the symbol in the label?"
Mocking the addition of the label symbol and its instruction address.
Question: "How do we determine the instruction address?"
Question: "How does SymbolTable add the entry to the symbol table?"
Aside: refactoring parser initialization and resetting into method.
  (Also renamed this process to reset instead of rewind.)
Implementing SymbolTable#add_entry.
Sanity check: Does it work?
- printing SymbolTable hashtable after first pass, for visual verification
Bonus
- deprecated class instance variables for constants, per best practice.
- refactoring Code class hashtables to be consistent, and
- demonstrating refactoring via "leaving the code in a better state" than
  when you first touched it, by using Code#validate in comp, dest, jump methods.
Implementing address retrieval from symbol table.
MILESTONE: Max.hack passes. Handling label symbols is complete.
Question, "Why does Rect.asm fail? How do we need to handle 'variable' symbols
           in A instructions? eg @foo"
Enhancing add_entry to handle variable labels. (With verbose Ruby.)
- includes variable_address
-- choosing to place this responsiblity in SymbolTable, with other explicit addresses
- demonstrating optional parameters in Ruby
Question: "How do we know it worked?"
- adding additional printing of symbol table entries after second pass.
MILESTONE: Passes Rect.asm.