librustdoc/html: recognize slices not to nest A tags.
1. A slice of parametrized type, say
BorrowedRef { ... Vector(Generic(T)) }, is rendered as
"<a href='primitive.slice.html'>&[T]</a>"
2. A slice of other types, say
BorrowedRef { ... Vector(int) }, is rendered as
"<a href='primitive.slice.html'>&[</a>
<a href='primitive.int.html'>int</a>
<a href='primitive.slice.html'>]</a>"
3. Other cases, say BorrowedRef { ... int }, are
rendered as same as before:
"&<a href='primitive.int.html'>int</a>"
Relevant W3C specs:
- http://www.w3.org/TR/html401/struct/links.html#h-12.2.2
12.2.2 Nested links are illegal
- http://www.w3.org/TR/html5/text-level-semantics.html#the-a-element
states A tag must not enclose any "interactive contents"
which include A tags themselves.