implement output buffering for GtGFF3Visitor
cosmetics
add script to check line-sortedness of GFF files
add first linesorted GFF3 out stream
add support for FASTA width and -retainids
resolve sorting
move linesorting check script to testdata directory
add testcases for -sortlines
ensure sorting by seqid and coords
Merge pull request #364 from satta/sorted_gff3

Implement line-based sorting of GFF3 output