Refactored variant loading so parallel processes read from the same VCF. With 8 procs, loading sites VCF took 45 min on laptop.
Refactored coverage loading. Moved call to ensure_index(..) to before loading data - this turned out to have faster runtimes. Added error handling to VCF parsing code.
Now running load_dbsnp, load_variants_file, load_base_coverage, and load_gene_models in parallel
Added random order of contigs to load faster
Added random order of contigs in sites VCF

Need to confirm that this works
Proper handling of hemizygous/homozygous on X/Y
Minor fixes