[Typing-sig] Self type PEP

Hello everyone, We've drafted a PEP for a `Self` type. This provides a painless, readable way to annotate methods and classmethods that return `self` or `cls(...)` respectively. We found that this pattern comes up a lot in real-world code; for example, typeshed uses this around 40% as often as popular types such as Dict or Callable. Please share your feedback in the Google Doc: https://docs.google.com/document/d/1ujuSMXDmSIOJpiZyV7mvBEC8P-y55AgSzXcvhrZc... Best, S Pradeep Kumar James Hilton-Balfe Original thread: https://mail.python.org/archives/list/typing-sig@python.org/thread/SJAANGA2C...