Customized instruction set (with compatibility mode)

Customized instruction set (with compatibility mode)

1) Removed done_o signal, replaced with HALT instruction
2) Nuked delay slot (muck) and removed related instructions
3) Added RTI, RTS, BRL, BRLI, BRALI instructions
4) Recoded CMP instruction, added CMPI
5) Added macro for compatibility mode (recognizes original instruction set,
   i.e delay slot, original CMP instruction - and keeps HALT, and some new
   instruction where blocking them would require additional logic (extra
   no delay variants of existing instructions)
6) Simplified flushing
7) Given patched binutils, gcc and newlib, mb-dasm has been removed for redundancy

Signed-off-by: Martin Meloun <meloumar@cmp.felk.cvut.cz>