Remove the Initial trait

[tertsdiepraam]

The Initial trait was unnecessary complexity. Instead of requiring it, the library now does not make any assumptions about the initial state of the settings. Instead, parse and try_parse take a self parameter that represents the initial state. The easiest way to do this is still via Default (i.e. Settings::default().parse(...)), but that is not necessary. This allows us to delete a bunch of code! Leaving this as a draft because I just wrote this very quickly had should look this over one more time later.

[sylvestre]

needs to be rebased :)

[tertsdiepraam]

Done!