cpp files: is_X_chr -> is_x_chr

  - Also, don't use "ignored" as arg name in riself/risib;
    use the regular arg name even if unused
speed up tests of calcgenoprob and estmap
add map functions and their inverses, within R
Major revisions to insert_pseudomarkers; need more tests

 - can take an arbitrary map of pseudomarkers

 - split up some larger functions into smaller ones
insert_pseudomarkers: rename some arguments; forgot to update .Rd file
Add test of insert_pseudomarkers with custom pseudomarker map
convert2cross2 and read_cross2: ensure cross_info is integer (not logical)
read_cross2: check if file exists before attempting to read
calc_genoprob now takes proper cross2 object
convert2cross2: had included sex not is_female, and geno was double not int
calc_genoprob: add explanation for 'cross' param
est_map now takes proper cross2 object
Revise tests of est_map for new version of function
fix stupid bug in calc_genoprob: need to subtract 1 from index; maybe I should just do that in advance
fix tests for new versions of calc_genoprob and est_map
Revise index for _pseudomarker_map to by {0, ..., n_mar-1}