Implement the \x86 TUPLE2 opcode for decoding, operation 'Build a two-tuple
out of the top two items on the stack.'
Add test for opTuple2 decode
d.marker() doesn't seem to be the proper way to get stack length, use #'len on d.stack for #'loadTuple2 instead
Merge pull request #8 from Sean-Der/implement-tuple2-decode

Implement the TUPLE2 Opcode
Implement Tuple1 and Tuple3 opcodes.