* Updated Invoicing APIs [145](https://github.com/paypal/PayPal-Pytho…

…n-SDK/pull/145).

* Fixed syntax error & pep8 formatting [#152](https://github.com/paypal/PayPal-Python-SDK/pull/152).

* Enabled Replace for Payment [#144](https://github.com/paypal/PayPal…

…-Python-SDK/pull/144).

* Enabled Third Party Invoicing [#138](https://github.com/paypal/PayP…

…al-Python-SDK/pull/138).

* Enabled Headers in Oauth calls [#134](https://github.com/paypal/PayPal-Python-SDK/pull/134).
* Updated requirements [#126](https://github.com/paypal/PayPal-Python-SDK/pull/126).
* Make sure the subscription start_date is in the future [#125](https://github.com/paypal/PayPal-Python-SDK/pull/125).
* Fix variable name typo in payment test [#117](https://github.com/paypal/PayPal-Python-SDK/pull/117).

Update logging

Update TLS warning message with site info

patch for checking against openssl 1.0.1

Add security test sandbox endpoint, tls warning and user agent update