Currently, an org block that has no output (e.g., `foo = 5`) never
clears the `[....]` upon block completion.
Also, no `:session` should default to localhost.
M-x customize-group RET ein
Toggle Ein:Polymode
Avoid trying to emulate jump-to-definition, eldoc, and autocompletion
functionalities that Elpy will always do better.
Fixes#497#482#418