use RegisterFile in Decoder
merge commit remove unused port from datamemory
add hazardunit file
add stall (IFID.write) to if_id_buff
move RegisterFile to a new source file
added new RegisterFile source file to project
Merge branch 'decoder' into skinny-decoder

Conflicts:
	Lab3.xise
revert top module to CPU
bug fix in EX forwarding unit
bug fix in RegisterFile
bug fix in decoder
fix cases for NOP in Control unit
minor changes in CPU
prevent writing to reg0
bug fix in forwarding unit
added forwarding for sw (storeword)
added missing SLT in ALU
changed instruction and data
change datamemory to use word
comment out alu MUL and DIV