This emulator provides a rough way for binaries designed for this CPU to be
executed in a virtual/emulated CPU for testing purposes. This patch also adds
a small test setup for automated assembly, execution and checking of register
postconditions for programs.

This adds a support script for future expansion of an asm->disasm->asm
series of tests, which will at minimum ensure some parity between the
assembler and disassembler. Lower level tests to ensure correct behaviour
rather than just symmetrical behaviour belong in another set of tests.

This patch also fixes the assembler's behaviour around numeric labels.
Many other assemblers support entirely numeric labels, and the output
of the disassembler includes them. The assembler has been adjusted to
lex a probably-numeric as a label if it is at the start of the line.
Otherwise, old label behavour and old numeric behaviour is left in
place.