Add docs for nmod_poly_gcdinv and nmod_poly_invmod
Add docs for nmod_poly_gcdinv and nmod_poly_invmod

wbhart/flint2,jpflori/flint2,wbhart/flint2,dsroche/flint2,dsroche/flint2,wbhart/flint2,dsroche/flint2,fredrik-johansson/flint2,fredrik-johansson/flint2,fredrik-johansson/flint2,dsroche/flint2,jpflori/flint2,jpflori/flint2,jpflori/flint2