Use git to get whipper's version

This essentially a copy of code from spotify2musicbrainz:
59157165c4

Given that that code is in GPLv3 (and I'm its author :)), it should be
fine to use. It is mostly boilerplate from upstream documentation
anyway: https://pypi.org/project/setuptools-scm/

Should fix https://github.com/whipper-team/whipper/issues/337

Signed-off-by: Frederik “Freso” S. Olesen <freso.dk@gmail.com>

setup.py

@@ -1,15 +1,15 @@
 from setuptools import setup, find_packages
-from whipper import __version__ as whipper_version
 
 setup(
     name="whipper",
-    version=whipper_version,
+    use_scm_version=True,
     description="a secure cd ripper preferring accuracy over speed",
     author=['Thomas Vander Stichele', 'The Whipper Team'],
     maintainer=['The Whipper Team'],
     url='https://github.com/whipper-team/whipper',
     license='GPL3',
     packages=find_packages(),
+    setup_requires=['setuptools_scm'],
     entry_points={
         'console_scripts': [
             'whipper = whipper.command.main:main'