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

Ah ok, that's clear.
Just a quick question/suggestion: htslib has \#define  macros for type of variant: VCF_REF, VCF_SNP, VCF_INDEL etc. Would it be useful to add a macro for VCF_NON_REF? This variant type would be set in bcf1_t.d.var.type during unpack.