1. Modified vcf_parse to update rlen only when an END INFO tag is seen -

Issue: https://github.com/broadinstitute/gamgee/issues/191
1. Modified vcf_parse to update rlen only when an END INFO tag is seen -the END tag is NOT encoded into v->shared.s
2. Modified vcf_write to add END INFO tag if required

I assumed that the END tag is only useful for genomic intervals with the single alternate allele <NON_REF>. Is it possible to have a genomic interval with 3 alleles (reference + 2 alternate)? Single site records with multiple alleles are possible, but for these records the END tag is useless.