Fixed #631 -- deprecate all of OpenSSL.rand (#658)

* Fixed #631 -- deprecate all of OpenSSL.rand

* syntax fix

* flake8
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index ab1072d..f42f4d9 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -18,7 +18,8 @@
 Deprecations:
 ^^^^^^^^^^^^^
 
-*none*
+- Deprecated ``OpenSSL.rand`` - callers should use ``os.urandom()`` instead.
+  `#658 <https://github.com/pyca/pyopenssl/pull/658>`_
 
 
 Changes:
diff --git a/doc/api.rst b/doc/api.rst
index 826ec4d..b5ca3f2 100644
--- a/doc/api.rst
+++ b/doc/api.rst
@@ -14,5 +14,4 @@
    :maxdepth: 2
 
    api/crypto
-   api/rand
    api/ssl
diff --git a/doc/api/rand.rst b/doc/api/rand.rst
deleted file mode 100644
index 47460a8..0000000
--- a/doc/api/rand.rst
+++ /dev/null
@@ -1,41 +0,0 @@
-.. _openssl-rand:
-
-:mod:`rand` --- An interface to the OpenSSL pseudo random number generator
-==========================================================================
-
-.. warning::
-   Functions from this module shouldn't be used.
-   `Use urandom <https://sockpuppet.org/blog/2014/02/25/safely-generate-random-numbers/>`_ instead.
-
-
-.. py:module:: OpenSSL.rand
-   :synopsis: An interface to the OpenSSL pseudo random number generator
-
-
-This module handles the OpenSSL pseudo random number generator (PRNG) and declares the following:
-
-.. autofunction:: add
-
-.. autofunction:: bytes
-
-.. autofunction:: cleanup
-
-.. autofunction:: load_file(filename[, bytes])
-
-.. autofunction:: seed
-
-.. autofunction:: status
-
-.. autofunction:: write_file
-
-
-.. function:: screen
-
-    Add the current contents of the screen to the PRNG state.
-
-    Availability: Windows.
-
-    :return: :obj:`None`
-
-
-.. autoexception:: Error
diff --git a/src/OpenSSL/rand.py b/src/OpenSSL/rand.py
index cf2053f..e2f6373 100644
--- a/src/OpenSSL/rand.py
+++ b/src/OpenSSL/rand.py
@@ -2,6 +2,7 @@
 PRNG management routines, thin wrappers.
 """
 
+import warnings
 from functools import partial
 
 from six import integer_types as _integer_types
@@ -13,6 +14,12 @@
     path_string as _path_string)
 
 
+warnings.warn(
+    "OpenSSL.rand is deprecated - you should use os.urandom instead",
+    DeprecationWarning, stacklevel=3
+)
+
+
 class Error(Exception):
     """
     An error occurred in an :mod:`OpenSSL.rand` API.