FEATURE: Eliminate YAML dependency

[ajjackson]

YAML is slow and is an annoying dependency to add on systems that don't otherwise use Python 3 for anything. A simpler text format using a default parser would be fine. Configparser looks like the way to go

There aren't many users at the moment, so we can probably afford to make the change now. If made later, a script should probably be provided to migrate existing YAML files to the new format.

[ajjackson]

Done, and version number bumped to 0.3.0 to reflect API breakage.