Type hints

boltons have some nice functionality but it would be very handy if it also had type hints. From https://github.com/mahmoud/boltons/pull/318 it seems you are open to type hints, but I just want to confirm this, and check if you have any specific preferences for how they should be added.

From what I gather from the linked issue:

• You prefer type hints in .py files (i.e. embedded) as opposed to having them in separate .pyi files
• You want validation in CI

Is there any thing more I should consider before working on it?