missing impls in std::str::Pattern docs

[durka]

Some of the impls of Pattern disappeared from the std docs starting in beta. Compare:

• http://doc.rust-lang.org/std/str/pattern/trait.Pattern.html (stable docs, impls shown)
• http://doc.rust-lang.org/nightly/std/str/pattern/trait.Pattern.html (nightly docs, impls missing)

They are also missing from the stable (and nightly) docs of core.

[bluss]

Related to #29503. I'm surprised, I would not call for CharEqPattern<C> where C: CharEq a blanket impl.