It's not very good, but it supports all of the options by the
previous far-worse Makefile configure targets, and also now supports
out-of-tree builds.
Also include the relevent updates to the .buildbot script and
.gitignore.
Though not a real register, the operand "(hl)" fits in
better with the 8-bit registers than it does with the
sixteen bit ones. As such, move its definition.
Also, define useful values for the 8-bit operands rather
than arbitrary ones.
