beginnings of cross class / factory for HMM
Remove a couple of "virtual"s from cross_bc/f2.h
src/cross: setting of no. genotypes
working on cross class definitions
Add BC::geno
risib/riself cross functions for HMM

 + a bunch of minor things like Rcpp:exception
cosmetic changes
enums to clean up cross_*.cpp code a bit
get_permutations -> permute_nvector

 - had function get_permutation (like sample(n)) and get_permutations;
   changed latter to permute_nvector
 - added permute_ivector
 - export only the permute_nvector and permute_ivector that do multiple
   permutations
 - revise tests to match
clarify comment re cross factory [skip ci]
Merge branch 'master' into devel
revise risib/riself functions
Add check_geno function; fix up cross_bc.cpp
fix up cross_riself
Fix up risib
RIself::check_geno: Small change
Revise cross_f2 stuff
Initial stab towards functions to test the basic HMM functions
Rcpp:exception -> throw std:range_error
Add code to allow testing the basic hmm functions from R