Make version available in code (#282)

It seems like there are multi ways to achieve that, all of them highliting
the importance of maintain a single source of truth for the version number.

More info: https://packaging.python.org/guides/single-sourcing-package-version/.

This PR includes one possible approach, open to discussion.

oidc_provider/version.py

@@ -0,0 +1 @@
+__version__ = '0.6.2'

setup.py

@@ -4,13 +4,16 @@ from setuptools import (
     setup,
 )
 
+version = {}
+with open("./oidc_provider/version.py") as fp:
+    exec(fp.read(), version)
 
 # allow setup.py to be run from any path
 os.chdir(os.path.normpath(os.path.join(os.path.abspath(__file__), os.pardir)))
 
 setup(
     name='django-oidc-provider',
-    version='0.6.2',
+    version=version['__version__'],
     packages=find_packages(),
     include_package_data=True,
     license='MIT License',