gproject: Get rid of some memory leaks

Thanks to Pavel Roschin.
gproject: One more memory leak fix

Thanks to Pavel Roschin
geniuspaste: Fix sign comparison warnings
pairtaghighlighter: Fix sign comparison warning
Fix and extend HACKING docs on writing build/someplugin.m4
geanyinsertnum PLUGIN_KEY_GROUP() -> plugin_set_key_group()
Merge branch 'master' of github.com:geany/geany-plugins
geanyextrasel PLUGIN_KEY_GROUP() -> plugin_set_key_group()
scope - ScpTreeStore documentation update
Fix a littly typo in French translation

Reported by Thierry.
scope - use ui_lookfind_widget(), sync [ ] Read only for the current document
Merge branch 'master' of github.com:geany/geany-plugins
scope - fix breakpoint tooltip rectangles for gtk+3
Merge remote-tracking branch 'upstream/master'