Add support for markdown to HTML conversion (matrix). Closes #663 (#670)

This uses our own gomatrix lib with the SendHTML function which
adds HTML to formatted_body in matrix.
golang-commonmark is used to convert markdown into valid HTML.

vendor/gitlab.com/golang-commonmark/markdown/reference.go

@@ -0,0 +1,173 @@
+// Copyright 2015 The Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package markdown
+
+import "strings"
+
+var referenceTerminatedBy []BlockRule
+
+func ruleReference(s *StateBlock, startLine, _ int, silent bool) bool {
+	lines := 0
+	pos := s.BMarks[startLine] + s.TShift[startLine]
+	max := s.EMarks[startLine]
+	nextLine := startLine + 1
+
+	if s.SCount[startLine]-s.BlkIndent >= 4 {
+		return false
+	}
+
+	src := s.Src
+
+	if src[pos] != '[' {
+		return false
+	}
+
+	pos++
+	for pos < max {
+		if src[pos] == ']' && src[pos-1] != '\\' {
+			if pos+1 == max {
+				return false
+			}
+			if src[pos+1] != ':' {
+				return false
+			}
+			break
+		}
+		pos++
+	}
+
+	endLine := s.LineMax
+
+	oldParentType := s.ParentType
+	s.ParentType = ptReference
+outer:
+	for ; nextLine < endLine && !s.IsLineEmpty(nextLine); nextLine++ {
+		if s.SCount[nextLine]-s.BlkIndent > 3 {
+			continue
+		}
+
+		if s.SCount[nextLine] < 0 {
+			continue
+		}
+
+		for _, r := range referenceTerminatedBy {
+			if r(s, nextLine, endLine, true) {
+				break outer
+			}
+		}
+	}
+
+	str := strings.TrimSpace(s.Lines(startLine, nextLine, s.BlkIndent, false))
+	max = len(str)
+
+	var labelEnd int
+	for pos = 1; pos < max; pos++ {
+		b := str[pos]
+		if b == '[' {
+			return false
+		} else if b == ']' {
+			labelEnd = pos
+			break
+		} else if b == '\n' {
+			lines++
+		} else if b == '\\' {
+			pos++
+			if pos < max && str[pos] == '\n' {
+				lines++
+			}
+		}
+	}
+
+	if labelEnd <= 0 || labelEnd+1 >= max || str[labelEnd+1] != ':' {
+		return false
+	}
+
+	for pos = labelEnd + 2; pos < max; pos++ {
+		b := str[pos]
+		if b == '\n' {
+			lines++
+		} else if !byteIsSpace(b) {
+			break
+		}
+	}
+
+	href, nlines, endpos, ok := parseLinkDestination(str, pos, max)
+	if !ok {
+		return false
+	}
+	href = normalizeLink(href)
+	if !validateLink(href) {
+		return false
+	}
+
+	pos = endpos
+	lines += nlines
+
+	destEndPos := pos
+	destEndLineNo := lines
+
+	start := pos
+	for ; pos < max; pos++ {
+		b := str[pos]
+		if b == '\n' {
+			lines++
+		} else if !byteIsSpace(b) {
+			break
+		}
+	}
+
+	title, nlines, endpos, ok := parseLinkTitle(str, pos, max)
+	if pos < max && start != pos && ok {
+		pos = endpos
+		lines += nlines
+	} else {
+		pos = destEndPos
+		lines = destEndLineNo
+	}
+
+	for pos < max && byteIsSpace(str[pos]) {
+		pos++
+	}
+
+	if pos < max && str[pos] != '\n' {
+		if title != "" {
+			title = ""
+			pos = destEndPos
+			lines = destEndLineNo
+			for pos < max && byteIsSpace(src[pos]) {
+				pos++
+			}
+		}
+	}
+
+	if pos < max && str[pos] != '\n' {
+		return false
+	}
+
+	label := normalizeReference(str[1:labelEnd])
+	if label == "" {
+		return false
+	}
+
+	if silent {
+		return true
+	}
+
+	if s.Env.References == nil {
+		s.Env.References = make(map[string]map[string]string)
+	}
+	if _, ok := s.Env.References[label]; !ok {
+		s.Env.References[label] = map[string]string{
+			"title": title,
+			"href":  href,
+		}
+	}
+
+	s.ParentType = oldParentType
+
+	s.Line = startLine + lines + 1
+
+	return true
+}