feat: exception route handlers

Author: vinniefalco

.github/workflows/ci-failure-auto-fix.yml

@@ -17,6 +17,9 @@ namespace boost {
 namespace http_proto {
 namespace detail {
 
+template<class...> struct make_void { typedef void type; };
+template<class... Ts> using void_t = typename make_void<Ts...>::type;
+
 template<class T>
 struct remove_cvref
 {

include/boost/http_proto/detail/type_traits.hpp

@@ -197,7 +197,11 @@ enum class error
 
     /** A dynamic buffer's maximum size would be exceeded.
     */
-    buffer_overflow
+    buffer_overflow,
+
+    /** An unhandled exception occurred while routing a request
+    */
+    unhandled_exception
 };
 
 // VFALCO we need a bad_message condition?