support more implied or mandatory options
use GtEncseq as GtBioseq backend
give proper error message when input sequence is empty
add .tags* files to .gitignore
return error message on invalid table ID
add include to header
add SNV feature type
cosmetics
add SNP annotation streams/visitors
add `gt snpper' tool
simplify text extents query
require lossless support when using '-encseq' option
bug fixes in '-encseq' access option
add test cases for sequence source combinations
version bump
update CHANGELOG