huge refactoring

app/handlers/context/errors.go

@@ -0,0 +1,13 @@
+package context
+
+type contentTypeNotFoundError struct{}
+
+func (e *contentTypeNotFoundError) Error() string {
+	return "The 'Content-Type' was not found in request context"
+}
+
+type converterNotFoundError struct{}
+
+func (e *converterNotFoundError) Error() string {
+	return "The converter was not found in request context"
+}