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/replacements.go

@@ -0,0 +1,229 @@
+// 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"
+
+func exclquest(b byte) bool {
+	return b == '!' || b == '?'
+}
+
+func byteToLower(b byte) byte {
+	if b >= 'A' && b <= 'Z' {
+		return b - 'A' + 'a'
+	}
+	return b
+}
+
+var replChar = [256]bool{
+	'(': true,
+	'!': true,
+	'+': true,
+	',': true,
+	'-': true,
+	'.': true,
+	'?': true,
+}
+
+func performReplacements(s string) string {
+	var ss []string
+
+	start := 0
+	for i := 0; i < len(s); i++ {
+		b := s[i]
+
+		if replChar[b] {
+
+		outer:
+			switch b {
+			case '(':
+				if i+2 >= len(s) {
+					break
+				}
+
+				b2 := s[i+1]
+
+				b2 = byteToLower(b2)
+				switch b2 {
+				case 'c', 'r', 'p':
+					if s[i+2] != ')' {
+						break outer
+					}
+					switch b2 {
+					case 'c':
+						if start < i {
+							ss = append(ss, s[start:i])
+						}
+						ss = append(ss, "©")
+					case 'r':
+						if start < i {
+							ss = append(ss, s[start:i])
+						}
+						ss = append(ss, "®")
+					case 'p':
+						if start < i {
+							ss = append(ss, s[start:i])
+						}
+						ss = append(ss, "§")
+					}
+					i += 2
+					start = i + 1
+					continue
+
+				case 't':
+					if i+3 >= len(s) {
+						break outer
+					}
+					if s[i+3] != ')' || byteToLower(s[i+2]) != 'm' {
+						break outer
+					}
+					if start < i {
+						ss = append(ss, s[start:i])
+					}
+					ss = append(ss, "™")
+					i += 3
+					start = i + 1
+					continue
+				default:
+					break outer
+				}
+
+			case '+':
+				if i+1 >= len(s) || s[i+1] != '-' {
+					break
+				}
+				if start < i {
+					ss = append(ss, s[start:i])
+				}
+				ss = append(ss, "±")
+				i++
+				start = i + 1
+				continue
+
+			case '.':
+				if i+1 >= len(s) || s[i+1] != '.' {
+					break
+				}
+
+				j := i + 2
+				for j < len(s) && s[j] == '.' {
+					j++
+				}
+				if start < i {
+					ss = append(ss, s[start:i])
+				}
+				if i == 0 || !(s[i-1] == '?' || s[i-1] == '!') {
+					ss = append(ss, "…")
+				} else {
+					ss = append(ss, "..")
+				}
+				i = j - 1
+				start = i + 1
+				continue
+
+			case '?', '!':
+				if i+3 >= len(s) {
+					break
+				}
+				if !(exclquest(s[i+1]) && exclquest(s[i+2]) && exclquest(s[i+3])) {
+					break
+				}
+				if start < i {
+					ss = append(ss, s[start:i])
+				}
+				ss = append(ss, s[i:i+3])
+				j := i + 3
+				for j < len(s) && exclquest(s[j]) {
+					j++
+				}
+				i = j - 1
+				start = i + 1
+				continue
+
+			case ',':
+				if i+1 >= len(s) || s[i+1] != ',' {
+					break
+				}
+				if start < i {
+					ss = append(ss, s[start:i])
+				}
+				ss = append(ss, ",")
+				j := i + 2
+				for j < len(s) && s[j] == ',' {
+					j++
+				}
+				i = j - 1
+				start = i + 1
+				continue
+
+			case '-':
+				if i+1 >= len(s) || s[i+1] != '-' {
+					break
+				}
+				if i+2 >= len(s) || s[i+2] != '-' {
+					if start < i {
+						ss = append(ss, s[start:i])
+					}
+					ss = append(ss, "–")
+					i++
+					start = i + 1
+					continue
+				}
+				if i+3 >= len(s) || s[i+3] != '-' {
+					if start < i {
+						ss = append(ss, s[start:i])
+					}
+					ss = append(ss, "—")
+					i += 2
+					start = i + 1
+					continue
+				}
+
+				j := i + 3
+				for j < len(s) && s[j] == '-' {
+					j++
+				}
+				if start < i {
+					ss = append(ss, s[start:i])
+				}
+				ss = append(ss, s[i:j])
+				i = j - 1
+				start = i + 1
+				continue
+			}
+		}
+	}
+	if ss == nil {
+		return s
+	}
+	if start < len(s) {
+		ss = append(ss, s[start:])
+	}
+	return strings.Join(ss, "")
+}
+
+func ruleReplacements(s *StateCore) {
+	if !s.Md.Typographer {
+		return
+	}
+
+	insideLink := false
+	for _, tok := range s.Tokens {
+		if tok, ok := tok.(*Inline); ok {
+			for _, itok := range tok.Children {
+				switch itok := itok.(type) {
+				case *LinkOpen:
+					insideLink = true
+				case *LinkClose:
+					insideLink = false
+				case *Text:
+					if !insideLink {
+						itok.Content = performReplacements(itok.Content)
+					}
+				}
+			}
+		}
+	}
+}