Short-hand predicates

[epage]

• code: take IntoCodePredicate
  • From<i32>
  • From<Predicate<i32>>
• stdin / stdout: take IntoOutputPredicate
  • From<str>
  • From<Predicate<str>>
  • From<[u8]>

[epage]

I'm marking as a breaking change out of concern because these kind of concrete API to conversion API changes have broken others in the past.