Rollup merge of #71767 - tshepang:stack-stuff, r=jonas-schievink

doc: make Stack and StackElement a little pretty

Also, fix rustdoc warnings.

src/libserialize/json.rs

@@ -1417,16 +1417,18 @@ enum ParserState {
 
 /// A Stack represents the current position of the parser in the logical
 /// structure of the JSON stream.
-/// For example foo.bar[3].x
+///
+/// An example is `foo.bar[3].x`.
 pub struct Stack {
     stack: Vec<InternalStackElement>,
     str_buffer: Vec<u8>,
 }
 
 /// StackElements compose a Stack.
-/// For example, StackElement::Key("foo"), StackElement::Key("bar"),
-/// StackElement::Index(3) and StackElement::Key("x") are the
-/// StackElements compositing the stack that represents foo.bar[3].x
+///
+/// As an example, `StackElement::Key("foo")`, `StackElement::Key("bar")`,
+/// `StackElement::Index(3)`, and `StackElement::Key("x")` are the
+/// StackElements composing the stack that represents `foo.bar[3].x`.
 #[derive(PartialEq, Clone, Debug)]
 pub enum StackElement<'l> {
     Index(u32),