CommentBuilder: remove typing.
Un-cythonize _builder.
Combine _builder.py into builder.py.
Add a timer around get_num_children.
Move get_num_children to cython file.
builder: fix up imports.
QueryBuilder: cleanup prewrap_fn argument retrieval.
CommentBuilder: take num as a constructor argument.

This follows the pattern of all other Builders.
Cleanup builder.py.
CommentBuilder: more timers.
morechildren: Pass num to CommentBuilder constructor.
Set children on MoreRecursion objects.

This ensures that the json representation will have valid name,
id, and children.