setup: Simplify release process using "versioneer"

Release process is now as simple as tagging a release, there
is no need to manually updates version in __init__.py

Most of the files enabling this process have been generated and/or
updated after:
1) pip install versioneer
2) adding "versioneer" section to setup.cfg
3) running "versioneer install"

For more details, see https://github.com/warner/python-versioneer/

.gitattributes

@@ -0,0 +1 @@
+wordcloud/_version.py export-subst

MANIFEST.in

@@ -0,0 +1,2 @@
+include versioneer.py
+include wordcloud/_version.py

setup.cfg

@@ -17,7 +17,14 @@ show-source = True
 # Maximum cyclomatic complexity allowed
 max-complexity = 14
 format = pylint
-exclude = .git,.idea,.eggs,__pycache__,doc/_build,doc/auto_examples,doc/conf.py,build
+exclude = .git,.idea,.eggs,__pycache__,doc/_build,doc/auto_examples,doc/conf.py,build,wordcloud/_version.py,versioneer.py
 
 [tool:pytest]
 addopts = -v --cov --cov-report xml --tb=short
+
+[versioneer]
+VCS = git
+versionfile_source = wordcloud/_version.py
+versionfile_build = wordcloud/_version.py
+style = pep440-post
+tag_prefix = ''

setup.py

@@ -1,13 +1,7 @@
-import re
 import io
 from setuptools import setup
 from setuptools.extension import Extension
-
-__version__ = re.search(
-    r'__version__\s*=\s*[\'"]([^\'"]*)[\'"]',  # It excludes inline comment too
-    io.open('wordcloud/__init__.py', encoding='utf_8').read()
-).group(1)
-
+import versioneer
 
 with io.open('README.md', encoding='utf_8') as fp:
     readme = fp.read()
@@ -16,7 +10,8 @@
     author="Andreas Mueller",
     author_email="[email protected]",
     name='wordcloud',
-    version=__version__,
+    version=versioneer.get_version(),
+    cmdclass=versioneer.get_cmdclass(),
     url='https://github.com/amueller/word_cloud',
     description='A little word cloud generator',
     long_description=readme,