DSS commands in the API

There are maybe hundreds of DSS commands that are not exposed as explicit API functions. Besides the long-term goal of exposing function sets for each DSS component, we also need to expose the commands. E.g. save circuit (https://github.com/dss-extensions/OpenDSSDirect.py/issues/89) doesn't seen to be exposed yet.

The APIs are the initial documentation most users find, so expanding them to include these will certainly help users in general.