Add an informative __main__.py (#620)

* Add an informative __main__.py

Give users an easy way to figure out what versions they're running.

* Why not more info!

* Add test

* No empty last line

* Make @alex happy

* DIAF Python 2.6

* Add cffi's version

* Make debug a module

* Add cryptography's compile-time OpenSSL
diff --git a/tests/test_util.py b/tests/test_util.py
index 78c97b5..91847e0 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -1,7 +1,7 @@
-from OpenSSL._util import exception_from_error_queue, lib
-
 import pytest
 
+from OpenSSL._util import exception_from_error_queue, lib
+
 
 class TestErrors(object):
     """
@@ -9,7 +9,7 @@
     """
     def test_exception_from_error_queue_nonexistent_reason(self):
         """
-        :py:func:`exception_from_error_queue` raises ``ValueError`` when it
+        :func:`exception_from_error_queue` raises ``ValueError`` when it
         encounters an OpenSSL error code which does not have a reason string.
         """
         lib.ERR_put_error(lib.ERR_LIB_EVP, 0, 1112, b"", 10)