Internal function to calculate MSY Reference Points
MSYCalcs(logF, M_at_Age, Wt_at_Age, Mat_at_Age, V_at_Age, maxage, R0x,
SRrelx, hx, opt = 1, plusgroup = 0)
log fishing mortality
Vector of M-at-age
Vector of weight-at-age
Vector of maturity-at-age
Vector of selectivity-at-age
Maximum age
R0 for this simulation
SRR type for this simulation
numeric. Steepness value for this simulation
Option. 1 = return -Yield, 2= return all MSY calcs
Integer. Default = 0 = no plus-group. Use 1 to include a plus-group
See opt