crecord: make enter move cursor down to the next item of the same type
Let's replace experimental.spacemovesdown with a separate key: Enter, since it
wasn't used for anything in crecord. Not sure if '\n' works on Windows though.
nextsametype() strictly only moves to items of the same type as the current
item. This, for example, allows to go over individual lines in a diff and skip
hunk and file headers (which would toggle multiple lines).