Fix linebreak handling in lxml parser and add better bullets

Fixes #218

mautrix_telegram/formatter/from_matrix/parser_common.py

@@ -22,10 +22,15 @@ from telethon.tl.types import TypeMessageEntity
 class MatrixParserCommon:
     mention_regex = re.compile("https://matrix.to/#/(@.+:.+)")  # type: Pattern
     room_regex = re.compile("https://matrix.to/#/(#.+:.+)")  # type: Pattern
-    block_tags = ("br", "p", "pre", "blockquote",
+    block_tags = ("p", "pre", "blockquote",
                   "ol", "ul", "li",
                   "h1", "h2", "h3", "h4", "h5", "h6",
                   "div", "hr", "table")  # type: Tuple[str, ...]
+    list_bullets = ("●", "○", "■", "‣")
+
+    @classmethod
+    def list_bullet(cls, depth: int) -> str:
+        return cls.list_bullets[(depth - 1) % len(cls.list_bullets)]
 
 
 ParsedMessage = Tuple[str, List[TypeMessageEntity]]