CI/CD improvements

[jhuntwork]

The development and CI/CD workflow is a little janky at the moment. There's a couple of issues:

• Larger packages that take a longer time to build (e.g., LLVM, Rust, Firefox) will time out in the current free tier of CircleCi.
• Each commit is expected to build one package. This isn't always desirable.
• Any solution for longer, automated builds will incur at least a momentary expense for launching cloud resources. This is fine, but then we probably want to protect against just any pull request from launching those.
• The flow or "rolling release" strategy between pacman repositories is currently stagnant as well.

I think all of the above makes it a prime time to also tie up loose ends in #377 #378 and #384. I'll let this be the driver for moving those things along, and I will probably begin making use of the https://github.com/merelinux organization.

I have also been toying with moving to Gitlab.com (while still mirroring here, probably). Anyone have any opinions on that?

[jhuntwork]

I found a way to improve build times for llvm using some careful parallelization setup in Circle CI and distcc. The build went from >1hr to 19min. There were still 10 minutes of packaging and compressing, but that's well within the time frame we need. I'll try to wrap up those changes shortly and get them merged.

[jhuntwork]

The fact that 1/3 of the build time for llvm is spent checking for package issues and compressing, spurs me on a bit more to look at makepkg alternatives. This relates to ideas expressed in #381. I will put that effort to the side for now, but I may look at swapping out makepkg sooner than later.