Added basic CONS implementation

Currently the implementation of CONS just makes the destination cell
refer to the two source registers. In the future there will probably
need to be distinctions made between lists and atoms so that atoms being
consed into a list can be dereferenced instead of just pointing to the
original atom (which would currently be interpreted as a nested list).
Removed erroneous extra argument to setNil

The extra argument was the result of a copy paste error.