Switches all the strings to single quotes.
Switches an upstream link to the master branch.
Switches the upstream link of the docker binary.
Adds helper files.

+ docker.service is now downloaded from upstream.
+ docker.bash and docker.zsh are downloaded from upstream.
+ docker.install manages the docker group, reloads systemd configuration
and gives directions to start using Docker.
+ docker.sysctl gives directions to enable IPv4 forwarding.
Updates .gitignore for new helper files.
Adds a ChangeLog.
Adds missing semicolons.
Clarifies some post-installation wording.
Removes an undesirable tab.