Rustdoc (rustdoc_ng) should hide priv items and methods by default

[bluss]

Rustdoc should hide private and should be private items like statics, functions, structs where priv or non-pub is effectively malfunctioning today.

Lots of non-pub methods, functions, structs are now showing up in the official Trunk documentation, and thanks to bugs it's possible to use some of these as well (for example std::hashmap::resize_at is can be called).

• Documentation is easier to understand if only pub items are shown
• We want to avoid users starting to rely on non-pub items.

Tag #8125

[alexcrichton]

A good example of this is http://static.rust-lang.org/doc/master/std/hashmap/struct.HashMap.html, all of the methods at the top of the list shouldn't be there at all.

[alexcrichton]

This may or may not be a lot easier to accomplish with the outcome of #8215

[alexcrichton]

I'm actively working on this.