prepare release 4.2.0 (#1144)

Prepare release 4.1.1 (#1077)

prepare release 4.1.0 (#1072)

typing-extensions release 4.0.1

prepare release 4.0.0 (#941)

prepare release 3.10.0.2 (#873)

prepare release 3.10.0.1 (#863)

prepare release 3.10.0.0 (#805)

Revert last two changes; bump version to 3.7.4.3

This should address issues due to projects including 'typing' in their
requirements.txt file without a version constraint on Python (or
pinning to 3.7.4.1).

Bump version to 3.7.4.2