Add and use __version__ from main file

__version__ in main file of the package is one of the recomended
by Python Packaging User Guide.

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

Author: prmtl

pydot_ng/__init__.py

@@ -33,6 +33,7 @@
 
 __author__ = 'Ero Carrera'
 __license__ = 'MIT'
+__version__ = '1.0.1.dev0'
 
 PY3 = not sys.version_info < (3, 0, 0)
 

setup.py

@@ -1,5 +1,7 @@
 #!/usr/bin/env python
+import ast
 import os
+import re
 from codecs import open
 
 from setuptools import setup
@@ -10,13 +12,25 @@
 os.environ['COPYFILE_DISABLE'] = 'true'
 
 
+CURRENT_DIR = os.path.dirname(__file__)
+
+
+def get_version():
+    init_file = os.path.join(CURRENT_DIR, 'pydot_ng', '__init__.py')
+    _version_re = re.compile(r'__version__\s+=\s+(?P<version>.*)')
+    with open(init_file, 'r', encoding='utf8') as f:
+        match = _version_re.search(f.read())
+        version = match.group('version') if match is not None else '"unknown"'
+    return str(ast.literal_eval(version))
+
+
 with open('README.rst', 'r', 'utf-8') as f:
     readme = f.read()
 
 
 setup(
     name='pydot_ng',
-    version='1.0.1.dev0',
+    version=get_version(),
     description='Python interface to Graphviz\'s Dot',
     author='Ero Carrera',
     author_email='ero@dkbza.org',