Many AsciiExt imports have become useless thanks to the inherent ascii
methods added in the last commits. These were removed. In some places, I
fully specified the ascii method being called to enforce usage of the
AsciiExt trait. Note that some imports are not removed but tagged with
a `#[cfg(stage0)]` attribute. This is necessary, because certain ascii
methods are not yet available in stage0. All those imports will be
removed later.
Additionally, failing tests were fixed. The test suite should exit
successfully now.
Add method `String::retain`
Behaves like `Vec::retain`, accepting a predicate `FnMut(char) -> bool`
and reducing the string to only characters for which the predicate
returns `true`.
Behaves like `Vec::retain`, accepting a predicate `FnMut(char) -> bool`
and reducing the string to only characters for which the predicate
returns `true`.
Replaced by adding extra imports, adding hidden code (`# ...`), modifying
examples to be runnable (sorry Homura), specifying non-Rust code, and
converting to should_panic, no_run, or compile_fail.
Remaining "```ignore"s received an explanation why they are being ignored.
