add bytes.__mod__ (#1212)
add bytes.__mod__ (#1212)

Fixes python/mypy#3247

Also reviewed some related logic:
- __mod__ was added to both bytes and bytearray with PEP 461, which went into 3.5
- str.__mod__ takes only one argument, and the signature calls it "value"
- In Python 2, bytearray doesn't have __mod__ (and typeshed correctly omits it)
azag0/typeshed,euresti/typeshed,li-dan/typeshed