build-sys: fix distcheck
build-sys: clean up make clean
build-sys: assemble HTML in docs/html

The goal is to be able to preview how the documenation
will look when uploaded. Just point your browser at
   docs/html/man/index.html.
build-sys: generate links for html alias pages
man: use lxml for faster generation and pretty printing
systemd-python: provide version info to sphinx
html: make python docs look more like the rest

The result is ugly enough, I hope, to motivate someone with
design skills to fix it.