Add Jump instructions

Add instructions to cause a jump over a given number of instructions.
This will allow the addition of short-circuiting to the "and" and "or"
operators, as well as to the trinary operator.
Add a pop instruction

The "pop" instruction simply pops a single value off the stack.  This
can be used to discard one value off the stack that was used for a
conditional jump (JumpIf or JumpIfNot).