document origin of HCR values

[iantaylor-NOAA]

Values of the slope and intercept associated with the different HCRs are hardwired in
https://github.com/pacific-hake/runhakemse/blob/master/R/run_MSE_HCR.R#L24-L33
It would be good to better document the origin of these values (regression on the TACs set by the JMC and realized catch) and potentially replace with the code to do the regression (recognizing that updating the range of years over which the regression is applied would be a much bigger change).

[iantaylor-NOAA]

I think those values are the slope and intercept parameters from the linear models run on these lines:
https://github.com/pacific-hake/pacifichakemse/blob/master/R/calc_tac_estimated_vs_realized.R#L41-L42
but I haven't run the code in that file to confirm.

[iantaylor-NOAA]

Using this issue to note that the HCR options in Stock Synthesis (and in the hake assessment in particular) should be checked to make sure there is a match with the MSE calculation.

• check that fixed values are parameters from linear models as noted in comment above
• check that HCR calculation in SS matches MSE calculation (and compare with our write-ups and the hake treaty as well)