Move RnD sample programs to examples dir, rename test_data to example_data, add stubs for server and client

vendor/github.com/carlmjohnson/requests/errorkind.go

@@ -0,0 +1,20 @@
+package requests
+
+// ErrorKind indicates where an error was returned in the process of building, validating, and handling a request.
+// Errors returned by Builder can be tested for their ErrorKind using errors.Is or errors.As.
+type ErrorKind int8
+
+//go:generate stringer -type=ErrorKind
+
+// Enum values for type ErrorKind
+const (
+	ErrURL       ErrorKind = iota // error building URL
+	ErrRequest                    // error building the request
+	ErrTransport                  // error connecting
+	ErrValidator                  // validator error
+	ErrHandler                    // handler error
+)
+
+func (ek ErrorKind) Error() string {
+	return ek.String()
+}