v2.0

This release increments the IGD file format version from v2 to v3. There aren't really any VCF-related changes.

• Simplification of missing data handling. Previously, it was stored in its own table as sparse lists, and loaded all at once. For any non-trivial amount of missing data this could use a fair amount of RAM. Now it is just another row in the "regular" data rows.
• Each row can be either sparse or not. Sparse rows are list of sample indexes (like missing data was before). Non-sparse are bit vectors (like all the other data was before). This change makes the resulting file significantly smaller than before, for large datasets.
• The API for writing IGD data rows was simplifed.
• Faster processing of the bitvector representation.
• Example in igdpp for computing allele frequency.
• In-memory storage of allele values (the strings) was reworked to be significantly smaller. More than 6x smaller for most alleles.

v1.0

First release. VCF and VCF.GZ parsing. IGD parsing and creation.