Fixing typo and altering eqn 277 in GROUPR section

[BeyondEnervation]

• Added closing parentheses to the $(\sigma_0 - \sigma_{am})$ terms in the two integral terms
• Changed the smooth weight function $C(E)$ term from $(1-\beta)C(E)\sigma_{0}$ to $(1-\beta)C(E)(\sigma_{0} - \sigma_{am})$
  • This is consistent with its implementation in the NJOY16 groupr.f90 file, in genflx subr, line 5349 at time of writing
  • i.e. b(iz+3+li)=(sigz(iz)-sam)*wtf*(1-beta)
  • Also consistent I believe with the maths as the derivation of eqn. 277 suggests $\frac{\sigma_{e}}{\rho_{f}} = \sigma_0 - \sigma_{am}$
• I realise I should also recompile the njoy16.pdf file included but I don't think I have all the packages required so perhaps someone more competent could do that.