Improve or drop PKGBUILD support

[ikeydoherty]

PKGBUILD may offer simplicity, but in terms of being machine readable it's an absolute nightmare, and to fully parse it correctly requires execution of sub shells, thus the format in itself presents a security issue to even interact with it. (pkg_version functions and such)

Thus, we'll wait to see if anyone is interested in improving the PKGBUILD support, or drop it completely.

Primary issue is that Arch Linux is in no way interested in patch accounting [1], which makes it very difficult to have any form of support for the distribution itself.

[1] https://lists.archlinux.org/pipermail/arch-security/2015-April/000283.html