FlexiRPG 1.99.0

- Add a basic interface for managing miniatures.
- Fix non-square miniatures not being shown.
- Fix the server incorrecly handling out-dated clients.
- An incompatible protocol change to use content-based IDs (SHA-256
  hashes) to identify images. This is a backward-incompatible change
  and 1.99 servers only support 1.99 or later clients. Old map files
  and miniature libraries can be loaded and will be converted when
  saved.