basevar v2.6.8

BaseVar v2.6.8 Release Notes

This is a maintenance release focused on code hygiene, a correctness fix in
genotype phase encoding, and a hot-path serialization optimization. VCF output
is byte-for-byte identical to v2.6.7 except for the phase-separator fix
described below.

Bug Fixes

• VCF: encode genotypes as unphased in update_genotypes
• Allele values were always correct; only the / vs | phase separator was
  affected, and only for odd-index alleles (e.g. 0|1 → 0/1, 1|1 → 1/1).

Performance Improvements

• Caller: VCFTextLine::to_string() — eliminate per-line stringstream

Code Hygiene

1. Remove dead to_string() methods

2. Include-what-you-use cleanup

3. Rename caller struct VCFRecord → VCFTextLine