GTF fixes
update
Merge pull request #173 from tcarver/master

misc
Merge pull request #174 from satta/master

do not output empty GFF3 attributes
update
allow to exclude attributes from GFF3 output
introduce separate log scale option for coverage plots
Merge pull request #176 from tcarver/master

misc
Merge pull request #175 from satta/filter_qualifiers

allow to exclude attributes from GFF3 output