Redefine grammers for statements and expressions

[cyndyishida]

• parse structure is currently set up where it incorrectly labels expressions
  -i.e "#if x" is a statement and not a expression, the only expression is x, and the naming convention is incorrect
• find ways to condense safe_code_expr, code_expr, and valid_expr
• condense/fix whitespace around directives
• change abstract symbol tree to abstract syntax tree
• currently, if & if def has a stack of tuples where the value at index[0] has either the name of the macro for ifdef, and the if count number for the if directive. Needs to be refactored out