Add threadsafe/context.py

Author: peterhinch

v3/threadsafe/package.json

@@ -3,7 +3,7 @@
     ["threadsafe/__init__.py", "github:peterhinch/micropython-async/v3/threadsafe/__init__.py"],
     ["threadsafe/message.py", "github:peterhinch/micropython-async/v3/threadsafe/message.py"],
     ["threadsafe/threadsafe_event.py", "github:peterhinch/micropython-async/v3/threadsafe/threadsafe_event.py"],
-    ["threadsafe/threadsafe_queue.py", "github:peterhinch/micropython-async/v3/threadsafe/threadsafe_queue.py"]
+    ["threadsafe/threadsafe_queue.py", "github:peterhinch/micropython-async/v3/threadsafe/threadsafe_queue.py"],
     ["threadsafe/context.py", "github:peterhinch/micropython-async/v3/threadsafe/context.py"]
   ],
   "version": "0.1"