Increment version to v2.1.0 and add Python2.x deprecation warning (#458)

* Increment version and add Python2.x deprecation warning

Change test to actually test no warnings when on python3

flake8 compliant

* fix development status classifier

vcr/__init__.py

@@ -1,4 +1,6 @@
 import logging
+import warnings
+import sys
 from .config import VCR
 
 # Set default logging handler to avoid "No handler found" warnings.
@@ -9,6 +11,11 @@ except ImportError:
         def emit(self, record):
             pass
 
+if sys.version_info[0] == 2:
+    warnings.warn(
+        "Python 2.x support of vcrpy is deprecated and will be removed in an upcoming major release.",
+        DeprecationWarning
+    )
 
 logging.getLogger(__name__).addHandler(NullHandler())