Release 4.2.0 (pynamodb#715)

Update PyPI classifiers (production, py3.5) (pynamodb#710)

Update release notes for 4.0.0

Update release notes for 4.0.0b3 (pynamodb#659)

Update .travis.yml

Update type stubs for TTL feature (pynamodb#657)

Bump version to 3.4.0

Update release notes for 4.0.0b1 (pynamodb#611)

Stop using requests in favour of botocore & urllib3 (pynamodb#580)

Release notes for v3.3.3