Add Timer.RUN_NOW

h/t @nliviu

Closes: #10

CL: mjs: Add Timer.RUN_NOW

PUBLISHED_FROM=57f763bc28d87736b08d0bec65aaec274bba1a95

Author: Deomid Ryabkov

fs/api_timer.js

@@ -22,6 +22,7 @@ let Timer = {
   set: ffi('int mgos_set_timer(int,int,void(*)(userdata),userdata)'),
 
   REPEAT: 1,
+  RUN_NOW: 2,
 
   // ## **`Timer.now()`**
   // Return current time as double value, UNIX epoch (seconds since 1970).