Closes #12386. Removed 'pub mod' doc-comments in std::io's mod.rs file. Added summary doc-comments to test.rs, util.rs and stdio.rs.
tutorial: Missing tildes around .notrust block

Adds a missing tilde to the end and the start of two .notrust blocks.
Rename a few typeck method-related structures to UpperCamelCase.
Replace callee_id with information stored in method_map.
auto merge of #12571 : eddyb/rust/kill-callee-id, r=nikomatsakis

Every method call and overloaded operator had a `callee_id` that was be used to store the method type and type substitutions, that information is now stored in the `method_map`, alongside the method's origin.
auto merge of #12570 : kyrias/rust/master, r=cmr

Adds a missing tilde to the end and the start of two .notrust blocks.
auto merge of #12490 : zslayton/rust/doc-fix-12386, r=alexcrichton

Attn: @huonw 

Addresses #12386.