added crow

include/crow/exceptions.h

@@ -0,0 +1,14 @@
+#pragma once
+#include <stdexcept>
+
+namespace crow
+{
+    struct bad_request : public std::runtime_error
+    {
+        bad_request(const std::string& what_arg)
+            : std::runtime_error(what_arg) {}
+
+        bad_request(const char* what_arg)
+            : std::runtime_error(what_arg) {}
+    };
+}