added covregions.py (region-based cov analysis), regionboxplot.py (boxplot for region-based cov analysis) venn3way.py (three-way vcf intersect)
minor mods to shortngs.py lowcovmulti.py and panelcovplot.py
Merge branch 'master' of https://github.com/ARUP-NGS/Scrutil
updating validation scripts