setup: use setuptools_scm to automatically keep package version in sync with git tag

setup.py

@@ -2,7 +2,7 @@ from setuptools import setup
 
 setup(
     name='pyftpd-sink',
-    version='0.3',
+    use_scm_version=True,
     # description='',
     author='Fabian Peter Hammerle',
     author_email='fabian@hammerle.me',
@@ -31,5 +31,8 @@ setup(
     install_requires=[
         'pyftpdlib>=1.5.4',
     ],
+    setup_requires=[
+        'setuptools_scm',
+    ],
     tests_require=[],
 )