Incorrect data type in VCF headers for haplotype field

[ajw2329]

Hello! Thanks for writing such an excellent tool!

Currently, Heterogenesis represents haplotypes in generated VCFs using letters A, B, etc, but in the headers of the VCFs, the data type of this field is specified as "Integer" like so:
##FORMAT=<ID=HS,Number=1,Type=Integer,Description="Haplotypes">
This is written in heterogenesis_varincorp.py line 149

This causes type-aware parsers (e.g. vcfR) to incorrectly read in the haplotypes. I've submitted a pull request to address this, which merely changes "Integer" to "Character" (i.e. ##FORMAT=<ID=HS,Number=1,Type=Character,Description="Haplotypes">), which avoids the issue.

Thanks!