build: Bump version from 3.1.0 to 4.0.0

Bump the version for a final release.

Author: feanil

setup.py

@@ -7,7 +7,7 @@
 
 from setuptools import find_packages, setup
 
-version = '3.1.0'
+version = '4.0.0'
 description = __doc__.strip().split('\n')[0]
 this_directory = path.abspath(path.dirname(__file__))
 with open(path.join(this_directory, 'README.rst')) as file_in: