Change markdown rendering from blackfriday to goldmark (#9533)

* Move to goldmark

Markdown rendering moved from blackfriday to the goldmark.

Multiple subtle changes required to the goldmark extensions to keep
current rendering and defaults.

Can go further with goldmark linkify and have this work within markdown
rendering making the link processor unnecessary.

Need to think about how to go about allowing extensions - at present it
seems that these would be hard to do without recompilation.

* linter fixes

Co-authored-by: Lauris BH <lauris@nix.lv>

vendor/github.com/shurcooL/sanitized_anchor_name/.travis.yml

@@ -1,16 +0,0 @@
-sudo: false
-language: go
-go:
-  - 1.x
-  - master
-matrix:
-  allow_failures:
-    - go: master
-  fast_finish: true
-install:
-  - # Do nothing. This is needed to prevent default install action "go get -t -v ./..." from happening here (we want it to happen inside script step).
-script:
-  - go get -t -v ./...
-  - diff -u <(echo -n) <(gofmt -d -s .)
-  - go tool vet .
-  - go test -v -race ./...

vendor/github.com/shurcooL/sanitized_anchor_name/LICENSE

@@ -1,21 +0,0 @@
-MIT License
-
-Copyright (c) 2015 Dmitri Shuralyov
-
-Permission is hereby granted, free of charge, to any person obtaining a copy
-of this software and associated documentation files (the "Software"), to deal
-in the Software without restriction, including without limitation the rights
-to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-copies of the Software, and to permit persons to whom the Software is
-furnished to do so, subject to the following conditions:
-
-The above copyright notice and this permission notice shall be included in all
-copies or substantial portions of the Software.
-
-THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
-SOFTWARE.

vendor/github.com/shurcooL/sanitized_anchor_name/README.md

@@ -1,36 +0,0 @@
-sanitized_anchor_name
-=====================
-
-[![Build Status](https://travis-ci.org/shurcooL/sanitized_anchor_name.svg?branch=master)](https://travis-ci.org/shurcooL/sanitized_anchor_name) [![GoDoc](https://godoc.org/github.com/shurcooL/sanitized_anchor_name?status.svg)](https://godoc.org/github.com/shurcooL/sanitized_anchor_name)
-
-Package sanitized_anchor_name provides a func to create sanitized anchor names.
-
-Its logic can be reused by multiple packages to create interoperable anchor names
-and links to those anchors.
-
-At this time, it does not try to ensure that generated anchor names
-are unique, that responsibility falls on the caller.
-
-Installation
-------------
-
-```bash
-go get -u github.com/shurcooL/sanitized_anchor_name
-```
-
-Example
--------
-
-```Go
-anchorName := sanitized_anchor_name.Create("This is a header")
-
-fmt.Println(anchorName)
-
-// Output:
-// this-is-a-header
-```
-
-License
--------
-
--	[MIT License](LICENSE)

vendor/github.com/shurcooL/sanitized_anchor_name/go.mod

@@ -1 +0,0 @@
-module github.com/shurcooL/sanitized_anchor_name

vendor/github.com/shurcooL/sanitized_anchor_name/main.go

@@ -1,29 +0,0 @@
-// Package sanitized_anchor_name provides a func to create sanitized anchor names.
-//
-// Its logic can be reused by multiple packages to create interoperable anchor names
-// and links to those anchors.
-//
-// At this time, it does not try to ensure that generated anchor names
-// are unique, that responsibility falls on the caller.
-package sanitized_anchor_name // import "github.com/shurcooL/sanitized_anchor_name"
-
-import "unicode"
-
-// Create returns a sanitized anchor name for the given text.
-func Create(text string) string {
-	var anchorName []rune
-	var futureDash = false
-	for _, r := range text {
-		switch {
-		case unicode.IsLetter(r) || unicode.IsNumber(r):
-			if futureDash && len(anchorName) > 0 {
-				anchorName = append(anchorName, '-')
-			}
-			futureDash = false
-			anchorName = append(anchorName, unicode.ToLower(r))
-		default:
-			futureDash = true
-		}
-	}
-	return string(anchorName)
-}