* json: mark keyword-only args
Technically only true for Python 3.6+, but I didn't feel like copying
over the whole file just for Python 3.5. Let me know and I can.
* json: remove encoding from loads
This has been ignored and deprecated since 3.1 and will be removed in 3.9
It no longer even shows up in inspect.signature (in 3.8 it emits the
deprecation warning based on kwargs)
* json: update whitelists
Fixes the following issues:
* Literals rather than ... for default values
* None rather than ... for default value of typed variable
* Literals rather than ... # type for top level constants
* # Foo rather than # type: Foo
* return value of init not set to None
This is the other half of fixing #1115.
Also fixed the stub for JSONDecodeError and made it only exist in 3.5+.
Didn't otherwise review the exact attributes and types in the package.
