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/state_inline.go

@@ -0,0 +1,116 @@
+// 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 (
+	"bytes"
+	"unicode"
+	"unicode/utf8"
+)
+
+type StateInline struct {
+	StateCore
+
+	Pos          int
+	PosMax       int
+	Level        int
+	Pending      bytes.Buffer
+	PendingLevel int
+	Delimiters   []Delimiter
+
+	Cache map[int]int
+}
+
+func (s *StateInline) PushToken(tok Token) {
+	if s.Pending.Len() > 0 {
+		s.PushPending()
+	}
+	tok.SetLevel(s.Level)
+	s.PendingLevel = s.Level
+	s.Tokens = append(s.Tokens, tok)
+}
+
+func (s *StateInline) PushOpeningToken(tok Token) {
+	if s.Pending.Len() > 0 {
+		s.PushPending()
+	}
+	tok.SetLevel(s.Level)
+	s.Level++
+	s.PendingLevel = s.Level
+	s.Tokens = append(s.Tokens, tok)
+}
+
+func (s *StateInline) PushClosingToken(tok Token) {
+	if s.Pending.Len() > 0 {
+		s.PushPending()
+	}
+	s.Level--
+	tok.SetLevel(s.Level)
+	s.PendingLevel = s.Level
+	s.Tokens = append(s.Tokens, tok)
+}
+
+func (s *StateInline) PushPending() {
+	s.Tokens = append(s.Tokens, &Text{
+		Content: s.Pending.String(),
+		Lvl:     s.PendingLevel,
+	})
+	s.Pending.Reset()
+}
+
+func (s *StateInline) scanDelims(start int, canSplitWord bool) (canOpen bool, canClose bool, length int) {
+	pos := start
+	max := s.PosMax
+	src := s.Src
+	marker := src[start]
+	leftFlanking, rightFlanking := true, true
+
+	lastChar := ' '
+	if start > 0 {
+		lastChar, _ = utf8.DecodeLastRuneInString(src[:start])
+	}
+
+	for pos < max && src[pos] == marker {
+		pos++
+	}
+	length = pos - start
+
+	nextChar := ' '
+	if pos < max {
+		nextChar, _ = utf8.DecodeRuneInString(src[pos:])
+	}
+
+	isLastPunct := isMdAsciiPunct(lastChar) || unicode.IsPunct(lastChar)
+	isNextPunct := isMdAsciiPunct(nextChar) || unicode.IsPunct(nextChar)
+
+	isLastWhiteSpace := unicode.IsSpace(lastChar)
+	isNextWhiteSpace := unicode.IsSpace(nextChar)
+
+	if isNextWhiteSpace {
+		leftFlanking = false
+	} else if isNextPunct {
+		if !(isLastWhiteSpace || isLastPunct) {
+			leftFlanking = false
+		}
+	}
+
+	if isLastWhiteSpace {
+		rightFlanking = false
+	} else if isLastPunct {
+		if !(isNextWhiteSpace || isNextPunct) {
+			rightFlanking = false
+		}
+	}
+
+	if !canSplitWord {
+		canOpen = leftFlanking && (!rightFlanking || isLastPunct)
+		canClose = rightFlanking && (!leftFlanking || isNextPunct)
+	} else {
+		canOpen = leftFlanking
+		canClose = rightFlanking
+	}
+
+	return
+}