Gtk 3.22.x was split off to branch gtk-3-22 last month, but more
notably master is now off chasing gtk4 (and also not building on MSYS2).
Until everything shakes out, make gtk3-git build the stable branch,
but allow easy branch switching in case people want to try to experiment
with master.
* upgrade some broken packages
* correct some broken urls/checksums
* use secure urls where possible
* update PKGBUILD templates
* remove line-ending whitespace
* minor typos/fixes
Remaining md5sums either didn't download or
didn't pass checksum tests.