Rework configuration

[jcjones]

There's some inconsistent type checking here. Consider a library like Cerberus (https://github.com/pyeve/cerberus) which allows you to describe a config schema, enforce types, and define default setters where you need to merge values from args and yaml conditionally. You'll get consistent warning when a required input is of the wrong type or not present at all and it can be configured to purge data that's not part of the schema.

Originally posted by @beautifulentropy in #4 (comment)

[jcjones]

Also tackle #4 (comment)

[jcjones]

Also rehome it, per #4 (comment)