Typing syntax fixes (#1156)

* Typing syntax fixes

* Fix some function signatures that were messing with ellipsis
  for example, `fun(a, ...)` is not valid, but `fun(...)` is

* Dict value types - is that legal? (puzzle/provider.py)

* Ignore assigning instance to classes
  (singletons like Infinity in version/utils.py)

* Add basic mypy config

This configuration has all common settings like:

* strict Optional in functions that returns None

* ignore missing imports - this is usual thing

* Check code that has no typing annotation but uses typed classes/functions