Very basic UART emulation (write only)
Implemented rte instruction
Removed a declaration used for debug
Corrected interrupt dispatcher: set cr2 cause correctly
Implemented some of the shift instructions

sll[.c]
srl[.c]
sra[.c]
srai[.c]
Link after a br{cond}l if CU is set
neg[.c] was incorrectly emulated as not[.c]
Implemented mfsr and mtsr instructions