Save/load from disk (serializing / marshalling)
Format to be defined:

### Non-binary (will certainly have size issues)
  - JSON via Nim [marshal](https://nim-lang.org/docs/marshal.html) module
  - YAML via [NimYAML](https://nimyaml.org/serialization.html)
  - ...

### Binary
  - MessagePack via [msgpack4nim](https://github.com/jangko/msgpack4nim) or [msgpack-nim](https://github.com/akiradeveloper/msgpack-nim)
  - BSON via Nim [MongoDB](https://github.com/nim-lang/mongo/blob/master/lib/bson.nim)
  - Protocol Buffer via [protobuf-nim](https://github.com/ivankoster/protobuf-nim)
  - ...