Input: ALPS - add documentation for protocol versions 3 and 4

Also converts from using "old" and "new" to describe the already-known
protocols to using "version 1" and "version 2" to match the code.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: Chase Douglas <chase.douglas@canonical.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>