Include tests in package

It's needed for distro packaging in order to
run the test suite during the build. With that,
we can ensure the software is running properly
on the distribution.

setup.py

@@ -14,7 +14,7 @@ def read(fname):
                 'library that, among other things, supports JSON-RPC and zmq.',
     long_description=read('README.rst'),
     long_description_content_type="text/x-rst",
-    packages=find_packages(exclude=['tests', 'examples']),
+    packages=find_packages(exclude=['examples']),
     keywords='json rpc json-rpc jsonrpc 0mq zmq zeromq',
     author='Marc Brinkmann',
     author_email='[email protected]',