Mixpanel-py

* To reduce TLS cert friction, use requests rather than directly using urllib3.
Reinstate TLS cert validation by default. (103)
* Drop support for Python 3.4 in setup.py and testing matrix.
* Update readme references to mixpanel-utils project. (100)

* Disable urllib3 security warning only if not verifying server certs. (102)

* Do not verify server cert by default. (issue 97)

Bugfix release:
* Fix DeprecationWarning in urllib3 when using older argument name. (issue 93)
* Fix creation of urllib3.PoolManager under Python 2 with unicode_literals. (issue 94 - thanks, Hugo Arregui!)

A compatibility bugfix -- 4.8.0 broke subclassing compatibility with some
other libraries.

* Add api_secret parameter to import_data and merge methods. API secret is the
new preferred auth mechanism; the old API Key still works but is no longer
accessible in the Mixpanel settings UI. (ref: issues 85, 88)
* Add optional verify_cert param to Consumer.__init__ for those having trouble
with server cert validation. (ref: issue 86)