work in progess pacman proxy

## Usage

    export http_proxy=localhost:8080
    pacman -Syu

## Differences between [pacserve]

- This proxy doesn't require a modified pacman.conf, just that
  `http_proxy` is set
- This proxy should play nicely with systemd: be fully socket activated
  and only run when necessary (and if there's no traffic, shut itself
  down).

  [pacserve]: http://xyne.archlinux.ca/projects/pacserve/