CertificateBuilder accepts aware datetimes for not_valid_after and not_valid_before (#2920)

* CertificateBuilder accepts aware datetimes for not_valid_after and not_valid_before
These functions now accept aware datetimes and convert them to UTC

* Added pytz to test requirements

* Correct pep8 error and improve Changelog wording

* Improve tests and clarify changelog message

* Trim Changelog line length

* Allow RevokedCertificateBuilder and CertificateRevocationListBuilder to accept aware datetimes

* Fix accidental changelog entry
diff --git a/setup.py b/setup.py
index 3bacae7..b5c05df 100644
--- a/setup.py
+++ b/setup.py
@@ -62,6 +62,7 @@
     "pretend",
     "iso8601",
     "pyasn1_modules",
+    "pytz",
 ]
 if sys.version_info[:2] > (2, 6):
     test_requirements.append("hypothesis>=1.11.4")