Define API and implement an in-memory store.

pkg/api/api.go

@@ -0,0 +1,17 @@
+package api
+
+type User struct {
+	ID           string
+	PasswordHash string
+}
+
+type Device struct {
+	ID        string
+	PublicKey []byte
+}
+
+type Clipboard struct {
+	SenderDeviceID string
+	// Payloads maps DeviceIDs to base64 encoded data.
+	Payloads map[string]string
+}