Automate generation of reference docs with doxygen and breathe (#598)

* Make 'any' the default markup role for Sphinx docs

* Automate generation of reference docs with doxygen and breathe

* Improve reference docs coverage
diff --git a/docs/advanced/pycpp/object.rst b/docs/advanced/pycpp/object.rst
index 8e737cc..ae58876 100644
--- a/docs/advanced/pycpp/object.rst
+++ b/docs/advanced/pycpp/object.rst
@@ -33,6 +33,8 @@
 
 When conversion fails, both directions throw the exception :class:`cast_error`.
 
+.. _calling_python_functions:
+
 Calling Python functions
 ========================