Use m.css for generating doxygen docs (#49)

* Use m.css for generating doxygen docs

* pass CMake variables to Doxygen

* Setup config for Pages section

* show not explicitly documented objects

* update patch comment

* update comment on M_SHOW_UNDOCUMENTED

Co-authored-by: Lars Melchior <TheLartians@users.noreply.github.com>

documentation/conf.py

@@ -0,0 +1,19 @@
+DOXYFILE = 'Doxyfile'
+
+LINKS_NAVBAR1 = [
+    (None, 'pages', [(None, 'about')]),
+    (None, 'namespaces', []),
+]
+
+# Add your own navbar links using the code below.
+# To find the valid link names, you can inspect the URL of a generated documentation site.
+
+# LINKS_NAVBAR1 = [
+#     (None, 'pages', [(None, 'about')]),
+#     (None, 'namespaces', [(None, 'namespacegreeter')]),
+# ]
+#
+# LINKS_NAVBAR2 = [
+#     (None, 'annotated', [(None, 'classgreeter_1_1_greeter')]),
+#     (None, 'files', [(None, 'greeter_8h')]),
+# ]