brentp/vcfanno: fix END in non VCF files with ref and alt columns

v0.1.1 set number=1 when op=min see #40 fix when we get -0 converted to just '-' (#42) when an annotation bed file has a header with 'ref' or 'reference' and 'alt' or 'alternate', then match on the ref and alt values defined in those columns (not just on position as for bed). (vcfgo) allow double-digit number in header thanks @chapmanb correct END position when using ref and alt from a file with only a position (infer end as start + len(ref)) [thanks Tomas]