Small fixups

• I misstyped conf.d as init.d so no such scripts would be loaded.
• Added completions for --version, -v, --help and -h.
• Included version in the help output.
• Added tests.

First release

The intention of this was to have a simple plugin manager as possible. Inspired by the vim plugin plug.

The thought is that it should only use the fish default features and conventions.