Merge pull request #9 from singnet/senna-188-1

[das-atom-db/#188] Add attention broker's fetch() rpc

cache_network.proto

@@ -0,0 +1,15 @@
+syntax = "proto3";
+import "common.proto";
+package das;
+
+message MessageData {
+    string command = 1;
+    repeated string args = 2;
+    string sender = 3;
+    string receiver = 4;
+}
+
+service CacheNetwork {
+    rpc ping (Empty) returns (Ack) {}
+    rpc execute_message (MessageData) returns (Ack) {}
+}