Cleanups, README, and YAML generation
On our way to deploying docker-free-space to replace docker-gc, I rewrote the cloud-init YAML to be generated from Python instead of a single hand-written flat file. The reason for this is that YAML files do not support includes without using a template generator, so in order to deploy d-f-s through cloud-init, we would need to have inlined the script in cloud-init.yaml, updating it every time we changed the script.
As this involved creating more files to be sourced by the script, I took the opportunity to reorganise the repository into different directories for different usages, and also update the README (fixing #1 (closed)).