Move description of the Error trait to its own doc-comment
Move description of the Error trait to its own doc-comment

… rather than the module’s.

Remove code definition of the Error trait from its doc-comment

It was out of date, and rustdoc already shows the same information.

Add a default impl for Error::description and document it as deprecated.

It is redundant with Display while being much less flexible for implementors.

This is only a "soft" deprecation: it is not worth the hassle of a warning to existing users.

Tweak Error trait docs to reflect actual requirements

GBGamer/rust,GBGamer/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,GBGamer/rust,graydon/rust,aidancully/rust,GBGamer/rust,GBGamer/rust,graydon/rust,GBGamer/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust