docs: Set use_mathjax to true (#1251)

This avoids depending on latex for HTML formula output.

docs/build.gradle

@@ -64,6 +64,7 @@ doxygen {
     warn_logfile false
     warn_if_undocumented false
     generate_latex false
+    use_mathjax true
     html_timestamp true
     generate_treeview true
 }