Add support for converting checkmark unicode to latex symbol

This commit adds an entry to the list of tex escapes for the checkmark
unicode character. As part of this the use of the amssymb package is
added which is required for the checkmark symbol among others.

Closes #1959

sphinx/util/texescape.py

@@ -36,6 +36,7 @@ tex_replacements = [
     ('±', r'\(\pm\)'),
     ('→', r'\(\rightarrow\)'),
     ('‣', r'\(\rightarrow\)'),
+    ('✓', r'\(\checkmark\)'),
     # used to separate -- in options
     ('', r'{}'),
     # map some special Unicode characters to similar ASCII ones

sphinx/writers/latex.py

@@ -42,6 +42,7 @@ HEADER = r'''%% Generated by Sphinx.
 %(longtable)s
 \usepackage{sphinx}
 \usepackage{multirow}
+\usepackage{amssymb}
 %(usepackages)s
 %(numfig_format)s
 %(preamble)s