Summary after filtering VCF

[alexjironkin]

Once a VCF is filtered it would be useful to know some summary statistics about the filtered in/out positions.

For example: Number of positions failing different filters, that as a percentage of all positions.

filter,total_positions,percentage
mq_score:30,2000,0.002
min_depth:5,100000,0.1
min_depth:5,mq_score:30,500000,0.5

translating to 2000 positions failed mq_score:30 alone, 0.2% of the genome. 100000 failed min_depth alone, 10% of the genome, and 500000 bases failed both min_depth and mq_score, 50% of the genome.