Add event deserialization

This PR targets #375 (event deserialization).

Steps to do:

- [x] Event finalization -> compiling an `ws_event` from cached values
- [x] Recognition of "event" type
- [x] Support for event names
- [ ] Support for event values, including
    - [x] Direct: nil
    - [x] Direct: bool
    - [x] Direct: int
    - [x] Direct: string
    - [ ] Indirect: `ws_value` objects
- [ ] Tests