Use docker to build lots of packages

On a Linux system with Docker installed, you can now run the new `docker/build-all` script to automatically build binary packages for a slew of Linux distributions.  This currently includes:

  - Arch
  - CentOS 6 and 7
  - Debian wheezy
  - Ubuntu 12.04 LTS (precise) and 14.04 LTS (trusty)