Comment Change

1. Allow comment nodes to exist within the abstract
   syntax tree. Use cases:

   - Break list continuity.
   - Source code annotation in target markup languages.
   - Source code readability

2. Change definition of isObject. (Still `typeof` based,
   but includes functions and does not rely on instanceof.

3. Better exposure of toArray().

   toArray(arrayLike, startPos) ->
   toArray(arrayLike, startPos, endPos).