vcfconvert: vcf2hapslegendsample

* add vcf_to_hapslegendsample to vcfconvert
* output to stdout ir `-` or suppress with `.`
* change vcf_to_gensample to match the above
* fix some option parsing errors for `--tsv2vcf`
* add tests for convert
* failing the `--tsv2vcf` test at the moment due to bug parsing
  NULL (`--`) genotype. Should be skipping these lines, but
  printing with REF/ALT/GT from previous line.
* update convert manpage docs