pgloader.1.md: update formatting for ronn compatibility

Ronn is an alternative to pandoc for generating Groff man pages from
Markdown, and seems to produce better-looking man pages.
pgloader.1.md: remove trailing whitespace
Makefile: use ronn to generate docs
pgloader.1: include compiled man page for packaging convenience

Allows packaging systems like Homebrew to install manual pages
automatically for users without introducing a dependency on the manual
page build system.
Makefile: add standalone target that doesn't install quicklisp