gtruby: add some more attribute modifier methods
add gt_grep_nt()
do not create temp copies of descriptions while searching
add -matchdescstart and associated library code
add tests
gtlua: add support for -matchdescstart
extend option description
Merge pull request #317 from satta/matchdescstart

Address ambiguity in -matchdesc calls.
gtruby: correct use of gterror()
Merge pull request #324 from satta/set_attrib

gtruby: missing methods and fixes
rework LTRharvest X-drop code
Merge pull request #325 from satta/ltr_xdrop

rework LTRharvest X-drop code