Panda: context manager support (#1209)

* add __enter__ & __exit__ to Panda

* some examples

* another example

* even more

* use it here too

python/__init__.py

@@ -242,6 +242,12 @@ class Panda:
     # reset comms
     self.can_reset_communications()
 
+  def __enter__(self):
+    return self
+
+  def __exit__(self, *args):
+    self.close()
+
   def close(self):
     self._handle.close()
     self._handle = None