improve documentation of GT_DEPRECATED
consider gt_option_hide_default() for manpages
update CHANGELOG
fix definition in case of old clang

deprecated without msg should be available
update copyright notice
Merge pull request #502 from gordon/deprecateddoc

improve documentation of GT_DEPRECATED
Merge pull request #504 from gordon/changelog

update CHANGELOG
Merge pull request #505 from Garonenur/deprecated

fix definition in case of old clang
Merge pull request #503 from gordon/manpages

consider gt_option_hide_default() for manpages
changelog additions
Merge pull request #506 from Garonenur/changelog

changelog additions