TENTATIVE CU_HW skeleton for new ISA

TODO:
check if this thing works as soon as MS server is back online!
this should correctly identify all instructions, but doesn't actually generate CU signals yet. implement this.
add SIGN output from CU to ALU
fix- correctly implement SIGN signal
start implementing R-type control signals
Merge branch 'master' into dlx_impl

Conflicts:
	vhdlsim/CU_HW.vhd