rollup merge of #22094: alkor/cleanup-show-string

Rename several remaining `Show`s to Debug, `String`s to Display (mostly in comments and docs).
Update reference.md:
 - derive() no longer supports Zero trait
 - derive() now supports Copy trait

1 files changed, 1 insertions, 1 deletions

diff --git a/src/libcore/any.rs b/src/libcore/any.rs
index 40c2d82bf4b..462b6771b4a 100644
--- a/src/libcore/any.rs
+++ b/src/libcore/any.rs
@@ -27,7 +27,7 @@
 //! # Examples
 //!
 //! Consider a situation where we want to log out a value passed to a function.
-//! We know the value we're working on implements Show, but we don't know its
+//! We know the value we're working on implements Debug, but we don't know its
 //! concrete type.  We want to give special treatment to certain types: in this
 //! case printing out the length of String values prior to their value.
 //! We don't know the concrete type of our value at compile time, so we need to