x/net/html: Sync the html parser and atom with the current whatwg spec

The current documentation as well as set of atoms and attributes has gotten slightly out of sync with the current state of the WHATWG html5 specification. The change adds and removes several of the atoms and attributes, updates the documentation (such as steps numbering in inBodyEndTagFormatting) and modifies the spec URLs to https:// Change-Id: I6dfa52785858c1521301b20b1e585e19a08b1e98 Reviewed-on: https://go-review.googlesource.com/6173 Reviewed-by: Nigel Tao <nigeltao@golang.org> Cherry-picked-from: golang/net@3d87fd6

Author: dmitris

src/html/escape.go

@@ -56,7 +56,7 @@ var replacementTable = [...]rune{
 func unescapeEntity(b []byte, dst, src int) (dst1, src1 int) {
 const attribute = false
 
-// http://www.whatwg.org/specs/web-apps/current-work/multipage/tokenization.html#consume-a-character-reference
+// https://html.spec.whatwg.org/multipage/syntax.html#consume-a-character-reference
 
 // i starts at 1 because we already know that s[0] == '&'.
 i, s := 1, b[src:]