Fix a bunch of stuff.
From function arguments to semicolons, we've got it all.
Add new documentation comments to Sets_Recurse().
New arguments were added, so new comments were needed.
Complete Num_Construct().
Num_Construct() turns the X set into a set of two numbers: level and n. Level is given, and it returns n.
Fix more function arguments.
Sets_Recurse() (and, therefore, Start_Task()) need to know start and end because the master thread will no longer be sending out all of the messages.