Big Tetris Parties

[bitoffdev]

TL;DR This patch allows more than the previous 2 players to compete, and
makes many minor improvements.

---

• Add magic number to all messages to help catch any network issues
• Add message_type field to message wire header, and remove the message_type
  from the body of many messages
• Define new method, message_type_to_str, to print a human-readable message
  type for logging
• Create new helper method message_blob
• Declare a macro name "PLAYER_NAME_MAX_CHARS", and use it consistently to
  validate the player names.
• Refactor StringArray to take a max length and define the StringArray
  serialized header bytes using a struct
• Bump MAXMSG up to 2048
• Refactor serialize_state to use no more bytes that necessary, rather than
  using MAXMSG as before
• Server now sends reply to user registration to indicate success
• Remove unnecessary and barely-utilized Player->io_lock, since all writes are
  done with a single call, which POSIX guarantees to be thread-safe.
• Add additional safety checks to renderer so that the program doesn't throw
  nasty errors (segfault) when the renderer has not been properly initialized
• Fix bug in read_from_client that referenced the buffer rather than the cursor

[Nitepone]

Some questions before approving this for merge. But, I don't see anything urgent to change.

[bitoffdev]

Thanks for taking a look at my giant diff @Nitepone! 🙌 😍

I think this latest commit should address your comments.

[Nitepone]

LGTM