fix(latex-renderer): special chars in raw text

Escape some additional characters in raw text which have special meaning
in LaTeX and which previously hadn't been dealt with by
`latex-renderer`'s `render_raw_text`-method.

Refactor the corresponding test case along the lines of the other
parameterized test cases to improve the code's consistency.

mistletoe/latex_renderer.py

@@ -2,6 +2,7 @@
 LaTeX renderer for mistletoe.
 """
 
+import re
 import string
 from itertools import chain
 from urllib.parse import quote
@@ -78,11 +79,20 @@ def render_escape_sequence(self, token):
         return self.render_inner(token)
 
     def render_raw_text(self, token, escape=True):
-        return (token.content.replace('$', '\\$').replace('#', '\\#')
-                             .replace('{', '\\{').replace('}', '\\}')
-                             .replace('&', '\\&').replace('_', '\\_')
-                             .replace('%', '\\%')
-               ) if escape else token.content
+        """Escape all latex special characters $#&%_{}^~\\ within `token.content`.
+        """
+        if not escape:
+            return token.content
+
+        if not hasattr(self, 'raw_escape_chars'):
+            self.raw_escape_chars = re.compile('([$#&%_{}])')
+
+        content = token.content.replace('\\', '\\textbackslash')
+        content = self.raw_escape_chars.sub(r'\\\1', content)
+        # The \text* commands gobble up whitespace behind them -> {} to prevent that.
+        return content.replace('~', '\\textasciitilde{}') \
+                      .replace('^', '\\textasciicircum{}') \
+                      .replace('\\textbackslash', '\\textbackslash{}')
 
     def render_heading(self, token):
         inner = self.render_inner(token)

test/test_latex_renderer.py

@@ -71,10 +71,20 @@ def test_math(self):
         self._test_token('Math', expected,
                          children=False, content='$ 1 + 2 = 3 $')
 
-    def test_raw_text(self):
-        expected = '\\$\\&\\#\\{\\}'
-        self._test_token('RawText', expected,
-                         children=False, content='$&#{}')
+    @parameterized.expand([
+        ('$', '\\$'),
+        ('&', '\\&'),
+        ('#', '\\#'),
+        ('%', '\\%'),
+        ('_', '\\_'),
+        ('{', '\\{'),
+        ('}', '\\}'),
+        ('~', '\\textasciitilde{}'),
+        ('^', '\\textasciicircum{}'),
+        ('\\', '\\textbackslash{}'),
+    ])
+    def test_raw_text(self, target, expected):
+        self._test_token('RawText', expected, children=False, content=target)
 
     def test_heading(self):
         expected = '\n\\section{inner}\n'