Implement configuration pattern

[brianredbeard]

Mayday will reasonably have different options depending on the running platform. Furthermore, some users will want to change the default behavior. There are a number of mechanisms which could be used the implement this.

The simplest solution would be to use environment variables which could also be supplied as run-time arguments. This behavior would be familiar to users of etcd and fleet.

A second option would be the use of a configuration file (possibly at /etc/mayday/mayday.conf). Suggestions have been made for the configuration to be in either YAML or JSON format. As this is not a commonly edited file this could be a reasonable solution, though it raises issues about how the command should proceed when the configuration file does not lint correctly.

[weberr13]

I will keep these issues in mind as I lookk into it.

[brianredbeard]

THE DAY HAS COME!

Implemented via #36