Support for OCPP 2.0.1

[jacoscaz]

The next major version of this library should export two separate namespaces: OCPP16 (for OCPP 1.6-J) and OCPP20 (for OCPP 2.0.1). JSON schemas for the latter are already available through the compressed archives published by the OCPP alliance, converting them to the appropriate Typescript types shouldn't be too hard, though likely fairly tedious. json-schema-to-typescript might come in handy to bootstrap the effort and save some time.

Note to self: prefer small amounts of code duplication over hyper-complex, generic types. In big projects, this results in significantly less stress on the TS compiler and much faster build times.