snp and indel parsers unified

The code that makes the SNP and INDEL matrices binary and re-references alleles are now shared. This means that future updates will simultaneously occur for both SNP And INDEL matrices . Now only the annotation parsing steps, which are unique to the two types of data, are handled separately. Some unit tests were added to check that re-referencing steps occur as expected.

Initial version

Snitkitr has been in use for a while, but this is the first version tagged. Need to document a version for publication purposes. In the future versioning and tagging will hopefully occur at more frequent increments.