Homebrew support

Opening this PR more to spark a discussion about updating the build system for compatibility with Homebrew (and similar packagers), not so much to suggest this patchset is ready for merge.

Custom Homebrew tap to experiment with: https://github.com/benesch/homebrew-pgloader

Here's what's included:

1. [ronn](https://github.com/rtomayko/ronn)-formatted man pages. Already looking much better than pandoc, and I only did the bare minimum conversion.
1. Compiled man page (so Homebrew can install it without needing ronn).
1. `pgloader-standalone` makefile target that doesn't muck around with Quicklisp; assumes `buildapp` is available on the `PATH` and that ASDF modules all exist somewhere visible to ASDF. Homebrew has a strict policy against install scripts that download files, so Quicklisp is out if we ever want this formula to be part of Homebrew core.

(1) certainly isn't required, but I can't think of a way to avoid some form of (2) and (3). Let me know what you think!

(Both #42 and #44 relate to this PR.)