pacman 4 moves to [core]

Pacman 4 has landed in [core]! Thanks to 24 contributors producing 893 commits, you'll find many new features. The one explicitly worth calling out is PGP signing. However, until the last few details regarding database signing and keyring distribution are ironed out, this is disabled in pacman's default config. If you're interested trying out package verification, please refer to the documentation on the wiki about pacman-key or Allan's blog post.

As always, please make sure to merge your pacnew files!