Hide full search speed setting from public api

[KyleSiefring]

Thoughts?

[lu-zero]

why do you want it hidden and why aren't you just making the field pub(crate)?

[KyleSiefring]

Mostly want it hidden so that I can add and remove it without multiple api changes.

I felt that using pub(crate) might end up being too error prone. Example: accidentally exposing things by writing pub instead of pub(crate).

One alternative would be to save the speed level and seed internal settings inside the encoder, but not inside api exposed structures.

[lu-zero]

Until I cut a release any API you put move or change is fine and expected to change.

I'll make sure that the non-exhaustive and default() is in place tomorrow.