issue: first stab at loading reservation stations
issue: prototype complete
bak: remove prototype code that now has a proper implementation
issue: record optimization ideas for the future

The version I have now is easy to reason about. First goal is to get the CPU
working, and the I can come back and optimize it.  However, that is a long
ways off and I won't remember the issue unit by that point.  So, record the
ideas I have now and then I can potentially use them to make it faster later.
stub: ieu+mul units
dpram: infer it for now
issue: provide hint data to the register file
regfile: implemnt hint-driver register file
issue: connect to renamer, not decoder
renamer: start of interface
sim: modelsim now runs it also on my macbook
renamer: prototype complete
commit: first ideas
issue: reduce fan-out on mispredict
dpram: "old data" style for faster synthesis
pipeline: move backpressure from fifo to renamer

To make good use of reservation stations, we need to refill them
quickly once they are committed. Trying to use tokens in the FIFO
for this adds too many cycles of latency, wasting FIFO slots.

This commit puts the back-pressure in the renamer, which means
that a reservation station is only wasted for 2 cycles:
  useful data in station     (r_stat_reg*)
  commit decision            (r_done_regx => commit_stb)
  station readiness check    (r_ren_stb => s_ren_done_a)
renamer: is lower-left triangular, not LR
commit: prototype core for retiring instructions
fifo: adding glue to connect the pieces together
opa: enough pieces to run simulation!