ack parser.parse_ty change in quote_ty! (+ test)
auto merge of #19463 : kali/rust/master, r=alexcrichton

parse_ty() no longer takes a boolean parameter. quote_ty! implementation has not yet been modified accordingly. 

As a matter of fact, quote_ty! was not covered by tests. One test (called qquotes) references it, but it has been ignored for nearly one year and now need heavy refactoring.

quote_token.rs seemed like a good place to test quote_ty!, many other quote_*! macros were asserted there.
Prepared `StrExt` pattern using methods for stabilization
Made iterator-returning methods return newtypes
Adjusted some docs to be forwards compatible with a generic pattern API
Changed as many `StrExt` methods as possible to be default methods
in order to reduce the surface area of the code and to aid future
refactorings