- Deserializing an empty quoted string *will not* cause an error. Previously, this was causing an error.
- Deserializing an empty string *will* cause an error.
- Ensure keys are deserialized using all the rules applying to vals: add readkey() analogs to read().
- Added `KEYNIL` and `VALNIL` to `NodeType_e`, used by the parser to mark the key or val as empty. This changed the values of the `NodeType_e` enumeration.
- Added `NodeType::key_is_null()` and `NodeType::val_is_null()`.