Optional mips dependencies, update readme and yeet duplicated code

[AngheloAlf]

• Moved all the mips specific stuff to its own optional dependency group (see https://hatch.pypa.io/dev/config/dependency/#features and https://peps.python.org/pep-0508/#extras)
  • Because of this, splat now needs to be installed by explicitly specifying the features to use. So instead of installing splat64 you install splat64[mips]
  • I tried to explain this on the readme
• Updated the Quickstart to encourage using splat as a library.
• Remove duplicated code of create_config.py