Merge pull request MongoEngine#1952 from erdenezul/bump_v0.16.1

bump version 0.16.1

Merge pull request MongoEngine#1937 from bagerard/changelog

Bump version to 0.16.0 + update changelog

tweak tox.ini to pass tests

Fix travis's pypi release trigger

Merge pull request MongoEngine#1737 from CalgaryMichael/remove-pushall

Removing the usage of the '$pushAll' operator

Bump version to 0.15.0

v0.14.3 version bump

remove {nospam} from author_email & maintainer_email (PyPI doesnt val…

…idate those anymore)

v0.14.1 version bump + updated changelog

more docs tweaks [ci skip]