Implement rs.sendMessage()

Change-Id: I174f85760c4b34adbdd33f313c394842c13fba72
diff --git a/rsContext.cpp b/rsContext.cpp
index 1ade010..6d70308 100644
--- a/rsContext.cpp
+++ b/rsContext.cpp
@@ -859,6 +859,10 @@
     rsc->deinitToClient();
 }
 
+void rsi_ContextSendMessage(Context *rsc, uint32_t id, const uint8_t *data, size_t len) {
+    rsc->sendMessageToClient(data, RS_MESSAGE_TO_CLIENT_USER, id, len, true);
+}
+
 }
 }