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/Doxyfile b/docs/Doxyfile
new file mode 100644
index 0000000..4dc8bf0
--- /dev/null
+++ b/docs/Doxyfile
@@ -0,0 +1,19 @@
+PROJECT_NAME           = pybind11
+INPUT                  = ../include/pybind11/
+
+GENERATE_HTML          = NO
+GENERATE_LATEX         = NO
+GENERATE_XML           = YES
+XML_OUTPUT             = .build/doxygenxml
+XML_PROGRAMLISTING     = YES
+
+MACRO_EXPANSION        = YES
+EXPAND_ONLY_PREDEF     = YES
+EXPAND_AS_DEFINED      = PYBIND11_RUNTIME_EXCEPTION
+
+ALIASES                = "rst=\verbatim embed:rst"
+ALIASES               += "endrst=\endverbatim"
+
+QUIET                  = YES
+WARNINGS               = YES
+WARN_IF_UNDOCUMENTED   = NO