Improve conditional termination

[benbusby]

Right now while loops are terminated using the sequence 1999, while ifs are terminated using 2000. Neither is ideal for programs that need to use either of these values (i.e. setting a value to 2000 inside of an if statement would be problematic), but there has to be a numeric representation of terminating these sections that minimizes overlap with possible program values, while also not requiring a large number of digits to represent.