Rename or hide bincode::internal

[dtolnay]

It is confusing to have this module with a ton of public functionality in it. Am I allowed to use it? Is it reserved for internal bincode use? What makes it internal? Why is it public and visible in the docs?

[TyOverby]

It should probably be renamed back to "endian_choice"

[dtolnay]

I don't understand the logic for all of what is currently in internal but a simpler bincode::endian::Deserializer makes perfect sense to me. Things that have nothing to do with endian choice (like ErrorKind) should probably not be exported under endian_choice.