Avoid the need to use a patched version of MathJax

See https://github.com/mathjax/MathJax/pull/1453

setup/mathjax.py

@@ -21,7 +21,8 @@ from setup import Command, download_securely
 class MathJax(Command):
 
     description = 'Create the MathJax bundle'
-    MATH_JAX_URL = 'https://github.com/kovidgoyal/MathJax/archive/master.zip'
+    MATH_JAX_VERSION = '2.7.5'
+    MATH_JAX_URL = 'https://github.com/mathjax/MathJax/archive/%s.zip' % MATH_JAX_VERSION
     FONT_FAMILY = 'TeX'
 
     def add_options(self, parser):
@@ -33,7 +34,7 @@ class MathJax(Command):
         raw = download_securely(url)
         with ZipFile(BytesIO(raw)) as zf:
             zf.extractall(tdir)
-            return os.path.join(tdir, 'MathJax-master')
+            return os.path.join(tdir, 'MathJax-' + self.MATH_JAX_VERSION)
 
     def add_file(self, zf, path, name):
         with open(path, 'rb') as f:

src/pyj/read_book/mathjax.pyj

@@ -13,6 +13,18 @@ def get_url(mathjax_files, name):
     return ans
 
 def monkeypatch(mathjax_files):
+    StyleString = window.MathJax.Ajax.StyleString.bind(window.MathJax.Ajax)
+
+    def style_string(styles):
+        # replace the URLs in the generated stylesheet
+        return StyleString(styles).replace(/url\('?(.*?)'?\)/g, def (match, url):
+            if not url.endsWith('.woff'):
+                return match
+            url = get_url(mathjax_files, url)
+            ans = f"url('{url}')"
+            return ans
+        )
+
     orig = window.MathJax.Ajax.fileURL.bind(window.MathJax.Ajax)
     def file_url(file):
         ans = orig(file)
@@ -28,6 +40,7 @@ def monkeypatch(mathjax_files):
             print('WARNING: Failed to resolve MathJax file:', name)
         return ans
     window.MathJax.Ajax.fileURL = file_url
+    window.MathJax.Ajax.StyleString = style_string
     window.MathJax.Ajax.fileRev = def(file):
         return ''