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/blockquote.go

@@ -0,0 +1,233 @@
+// 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 "unicode/utf8"
+
+var blockquoteTerminatedBy []BlockRule
+
+func ruleBlockQuote(s *StateBlock, startLine, endLine int, silent bool) bool {
+	if s.SCount[startLine]-s.BlkIndent >= 4 {
+		return false
+	}
+
+	pos := s.BMarks[startLine] + s.TShift[startLine]
+	max := s.EMarks[startLine]
+	src := s.Src
+
+	if pos >= max {
+		return false
+	}
+	if src[pos] != '>' {
+		return false
+	}
+	pos++
+
+	if silent {
+		return true
+	}
+
+	initial := s.SCount[startLine] + pos - (s.BMarks[startLine] + s.TShift[startLine])
+	offset := initial
+
+	spaceAfterMarker := false
+	adjustTab := false
+	if pos < max {
+		if src[pos] == ' ' {
+			pos++
+			initial++
+			offset++
+			spaceAfterMarker = true
+		} else if src[pos] == '\t' {
+			spaceAfterMarker = true
+			if (s.BSCount[startLine]+offset)%4 == 3 {
+				pos++
+				initial++
+				offset++
+			} else {
+				adjustTab = true
+			}
+		}
+	}
+
+	oldBMarks := []int{s.BMarks[startLine]}
+	s.BMarks[startLine] = pos
+
+	for pos < max {
+		r, size := utf8.DecodeRuneInString(src[pos:])
+		if runeIsSpace(r) {
+			if r == '\t' {
+				d := 0
+				if adjustTab {
+					d = 1
+				}
+				offset += 4 - (offset+s.BSCount[startLine]+d)%4
+			} else {
+				offset++
+			}
+		} else {
+			break
+		}
+		pos += size
+	}
+
+	oldBSCount := []int{s.BSCount[startLine]}
+	d := 0
+	if spaceAfterMarker {
+		d = 1
+	}
+	s.BSCount[startLine] = s.SCount[startLine] + 1 + d
+
+	lastLineEmpty := pos >= max
+
+	oldSCount := []int{s.SCount[startLine]}
+	s.SCount[startLine] = offset - initial
+
+	oldTShift := []int{s.TShift[startLine]}
+	s.TShift[startLine] = pos - s.BMarks[startLine]
+
+	oldParentType := s.ParentType
+	s.ParentType = ptBlockQuote
+	wasOutdented := false
+
+	oldLineMax := s.LineMax
+
+	nextLine := startLine + 1
+	for ; nextLine < endLine; nextLine++ {
+		if s.SCount[nextLine] < s.BlkIndent {
+			wasOutdented = true
+		}
+		pos = s.BMarks[nextLine] + s.TShift[nextLine]
+		max = s.EMarks[nextLine]
+
+		if pos >= max {
+			break
+		}
+
+		pos++
+		if src[pos-1] == '>' && !wasOutdented {
+			initial = s.SCount[nextLine] + pos + (s.BMarks[nextLine] + s.TShift[nextLine])
+			offset = initial
+
+			if pos >= len(src) || src[pos] != ' ' && src[pos] != '\t' {
+				spaceAfterMarker = true
+			} else if src[pos] == ' ' {
+				pos++
+				initial++
+				offset++
+				adjustTab = false
+				spaceAfterMarker = true
+			} else if src[pos] == '\t' {
+				spaceAfterMarker = true
+
+				if (s.BSCount[nextLine]+offset)%4 == 3 {
+					pos++
+					initial++
+					offset++
+					adjustTab = false
+				} else {
+					adjustTab = true
+				}
+			}
+
+			oldBMarks = append(oldBMarks, s.BMarks[nextLine])
+			s.BMarks[nextLine] = pos
+
+			for pos < max {
+				r, size := utf8.DecodeRuneInString(src[pos:])
+				if runeIsSpace(r) {
+					if r == '\t' {
+						d := 0
+						if adjustTab {
+							d = 1
+						}
+						offset += 4 - (offset+s.BSCount[startLine]+d)%4
+					} else {
+						offset++
+					}
+				} else {
+					break
+				}
+				pos += size
+			}
+
+			lastLineEmpty = pos >= max
+
+			oldBSCount = append(oldBSCount, s.BSCount[nextLine])
+			d := 0
+			if spaceAfterMarker {
+				d = 1
+			}
+			s.BSCount[nextLine] = s.SCount[nextLine] + 1 + d
+
+			oldSCount = append(oldSCount, s.SCount[nextLine])
+			s.SCount[nextLine] = offset - initial
+
+			oldTShift = append(oldTShift, s.TShift[nextLine])
+			s.TShift[nextLine] = pos - s.BMarks[nextLine]
+
+			continue
+		}
+
+		if lastLineEmpty {
+			break
+		}
+
+		terminate := false
+		for _, r := range blockquoteTerminatedBy {
+			if r(s, nextLine, endLine, true) {
+				terminate = true
+				break
+			}
+		}
+
+		if terminate {
+			s.LineMax = nextLine
+
+			if s.BlkIndent != 0 {
+				oldBMarks = append(oldBMarks, s.BMarks[nextLine])
+				oldBSCount = append(oldBSCount, s.BSCount[nextLine])
+				oldTShift = append(oldTShift, s.TShift[nextLine])
+				oldSCount = append(oldSCount, s.SCount[nextLine])
+				s.SCount[nextLine] -= s.BlkIndent
+			}
+
+			break
+		}
+
+		oldBMarks = append(oldBMarks, s.BMarks[nextLine])
+		oldBSCount = append(oldBSCount, s.BSCount[nextLine])
+		oldTShift = append(oldTShift, s.TShift[nextLine])
+		oldSCount = append(oldSCount, s.SCount[nextLine])
+
+		s.SCount[nextLine] = -1
+	}
+
+	oldIndent := s.BlkIndent
+	s.BlkIndent = 0
+
+	tok := &BlockquoteOpen{
+		Map: [2]int{startLine, 0},
+	}
+	s.PushOpeningToken(tok)
+
+	s.Md.Block.Tokenize(s, startLine, nextLine)
+
+	s.PushClosingToken(&BlockquoteClose{})
+
+	s.LineMax = oldLineMax
+	s.ParentType = oldParentType
+	tok.Map[1] = s.Line
+
+	for i := 0; i < len(oldTShift); i++ {
+		s.BMarks[startLine+i] = oldBMarks[i]
+		s.TShift[startLine+i] = oldTShift[i]
+		s.SCount[startLine+i] = oldSCount[i]
+		s.BSCount[startLine+i] = oldBSCount[i]
+	}
+	s.BlkIndent = oldIndent
+
+	return true
+}