use customized rpc implementation, remove Tarpc & Tonic (#348)

This patch removes Tarpc & Tonic GRPC and implements a customized rpc framework, which can be used by peer rpc and cli interface.

web config server can also use this rpc framework.

moreover, rewrite the public server logic, use ospf route to implement public server based networking. this make public server mesh possible.

easytier/src/proto/error.proto

@@ -0,0 +1,34 @@
+syntax = "proto3";
+package error;
+
+message OtherError { string error_message = 1; }
+
+message InvalidMethodIndex {
+  string service_name = 1;
+  uint32 method_index = 2;
+}
+
+message InvalidService { string service_name = 1; }
+
+message ProstDecodeError {}
+
+message ProstEncodeError {}
+
+message ExecuteError { string error_message = 1; }
+
+message MalformatRpcPacket { string error_message = 1; }
+
+message Timeout { string error_message = 1; }
+
+message Error {
+  oneof error {
+    OtherError other_error = 1;
+    InvalidMethodIndex invalid_method_index = 2;
+    InvalidService invalid_service = 3;
+    ProstDecodeError prost_decode_error = 4;
+    ProstEncodeError prost_encode_error = 5;
+    ExecuteError execute_error = 6;
+    MalformatRpcPacket malformat_rpc_packet = 7;
+    Timeout timeout = 8;
+  }
+}