* Make sure private consts are stripped.
* Don't show a code block for the value if there is none.
* Make sure default values are shown in impls.
* Make sure docs from the trait are used if the impl has no docs.
Rather than (ab)using Debug for outputting the type in plain text use the
alternate format parameter which already does exactly that. This fixes
type parameters for example which would output raw HTML.
Also cleans up adding parens around references to trait objects.
Search results use the mapping found in `ItemType::to_static_str` for
the identifier, which could not be found on the page in the case of
associated items.
