Move cryptography.vectors to cryptography_vectors

All vectors are now stored in the subpackage in the vectors/ folder.

This package is automatically installed by setup.py test and will also
be uploaded with a matching version number by the PyPI upload task.
diff --git a/docs/doing-a-release.rst b/docs/doing-a-release.rst
index 8b37df7..fc88a91 100644
--- a/docs/doing-a-release.rst
+++ b/docs/doing-a-release.rst
@@ -10,6 +10,7 @@
 software.
 
 * Update the version number in ``cryptography/__about__.py``.
+* Update the version number in ``vectors/cryptography_vectors/__about__.py``.
 * Set the release date in the :doc:`/changelog`.
 * Do a commit indicating this.
 * Send a pull request with this.
@@ -33,5 +34,8 @@
     >>> import cryptography
     >>> cryptography.__version__
     '...'
+    >>> import cryptography_vectors
+    >>> cryptography_vectors.__version__
+    '...'
 
 Verify that this is the version you just released.