Closes #2361

Changes the cryptography requirement to !=3.4 as that release contains a bug with cyclical imports, see pyca/cryptography#5758 .

On the fly:

• re-adds docs for get_updates.read_latency, which apparently got lost somewhere around 2017 according to git blame
• Drops type hints from signature in docs, as they are hard to read and redundant (we document everything anyway)
• prettifies display of DefaultValue instances in signtures in docs
• makes disable_notification default to None instead of False. That has the same effect, we pass less stuff to TG (and it simplified tests)
• cleans up some foo = 'text' ' text continued' strings, probably leftovers from switching to black formatting

todo

• overhaul tests to strictly test defaults
• manually test stuff like answer_inline_query