Remove parse method from environment.
Runner uses the interpreter.
Rename some packages.

Besides being better organized, this is a step towards renaming macros
to special forms.
Rename macros to special forms.

Remove several references to the word macro.
Fix special form type name.
Add tail recursion by using continuations.

All special forms need to be altered to return the proper continuations
on tail calls.
Make 'and' and 'or' tail recursive.
Update TODO.
Rename variables in 'if' implementation for clarity.