Merge pull request gtk-rs#804 from sdroege/0.16-backports

0.16 backports

Update glib-build-tools version to 0.16.0

Update versions to 0.15.12

glib: Lower glib-macros version requirement to 0.15.10

glib: Depend on glib-macros 0.15.10

Update versions to 0.15.9

Update versions to 0.15.8

Update versions to 0.15.7

Update versions to 0.15.6

Merge pull request gtk-rs#531 from sdroege/0.15-backports

0.15 backports