Implement AND opcode
Implement EQ opcode
Implement GTE opcode

This is the first opcode that actually stresses the difference between
outwid() and width().
Implement NOT opcode

Note that this is the first opcode that loses some generality: LLVM
doesn't have a NOT so I had to use "xor ..., -1".  Most of the time
integer operations are all the same speed so it shouldn't matter, but
just be warned.
Add a "Fib" testcase

This calculates a series of Fibonacci numbers.  It's a bit more
complicated than the counter tests, but it's not a whole lot.