Fix pulldown diff

[GuillaumeGomez]

For the other output differences such as:

WARNING: rendering difference in `A DEFLATE-based stream compression/decompression library`
   --> src/lib.rs:1:0
    /html[0]/body[1]/p[4] Attributes differ in `a`: expected: `{"href": "bufread/index.html"}`, found: `{"href": "https://doc.rust-lang.org/std/io/trait.BufRead.html"}`

It's because in the old rustdoc markdown renderer, [read] == [Read]. So it's actually a good thing to have them.

EDIT: Ah, my bad. It's still an issue but a different one. Will be fixed in rustdoc so no need to change this.

EDIT of EDIT: The commonmark spec says:

As noted in the section on Links, matching of labels is case-insensitive (see matches).

You can see it here.

So I fixed them as well.