Added trove classifiers showing versions supported

This is how many tools are checking whether Python3 is supported.

Author: alex

setup.py

@@ -94,4 +94,13 @@ def run(self):
       packages=["ecdsa"],
       license="MIT",
       cmdclass={ "test": Test, "version": Version, "sdist": sdist },
-      )
+      classifiers=[
+          "Programming Language :: Python",
+          "Programming Language :: Python :: 2",
+          "Programming Language :: Python :: 2.6",
+          "Programming Language :: Python :: 2.7",
+          "Programming Language :: Python :: 3",
+          "Programming Language :: Python :: 3.2",
+          "Programming Language :: Python :: 3.3",
+      ],
+)