Add boilerplate for key server APIs (#1196)

Also add a README which outilnes how things will work.

clientapi/routing/keys.go

@@ -0,0 +1,40 @@
+// Copyright 2020 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package routing
+
+import (
+	"net/http"
+
+	"github.com/matrix-org/util"
+)
+
+func QueryKeys(
+	req *http.Request,
+) util.JSONResponse {
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: map[string]interface{}{
+			"failures":    map[string]interface{}{},
+			"device_keys": map[string]interface{}{},
+		},
+	}
+}
+
+func UploadKeys(req *http.Request) util.JSONResponse {
+	return util.JSONResponse{
+		Code: 200,
+		JSON: struct{}{},
+	}
+}