refactors and simplifies macro mappings

[zorkow]

• Refactors macro, command and environment maps in the packages to directly use methods provided by the MacroMap classes. This
  1. makes our code less dependant on string references
  2. should allow bundlers that minimize code (like Closure) to more efficiently replace method calls
• Retains legacy functionality by keeping an optional functionMap argument and checking if the ParseMethod reference is a string. This should ensure backward compatibility with third party packages.

[dpvc]

lgtm.