Put pkgver() function after $pkgver variable
Standardize git pkgver() function

Use a standard pkgver() implementation for git PKGBUILDs.

Two packages, minecraft-overviewer-git and minecraft-region-fixer-git,
continue to use their own due to an incompatible version scheme.
For these, simply change pkgver() to use similar `git` and `sed`
invocations.