Replace generic options hash with specific option.

In the past, we were supporting Ruby versions without named parameters and
we didn't know how many options will use for loading/parsing TOML.
Years have passed, and the interface is stable, so we are simplifying it.

This change will be useful for the adoption of Steep or defining types in Ruby 3 🎉

It shouldn't break to most users, but just in case it does, I released a patch version (v2.0.2) with the fix for trailing spaces, so anyone can use the fix without dealing with the incompatibility of this version may introduce.