Use towncrier to build the changelog (#3425)

.travis.yml

CONTRIBUTING.rst

MANIFEST.in

changelog.d/3324.removal

changelog.d/3327.bugfix

changelog.d/3332.misc

changelog.d/3334.feature

changelog.d/3340.doc

changelog.d/3341.misc

changelog.d/3344.feature

changelog.d/3347.misc

changelog.d/3348.misc

changelog.d/3349.bugfix

changelog.d/3355.bugfix

changelog.d/3356.misc

changelog.d/3363.bugfix

changelog.d/3371.bugfix

changelog.d/3372.feature

pyproject.toml

tox.ini