Move version string to the python code

This way the python module "knows" its own version. To avoid duplication,
read the value back from setup.py. The reader function only needs to
support the specific format used in the code, so it can be very simplistic.

rust2rpm/__init__.py

@@ -1,2 +1,4 @@
 from .metadata import *
 from . import licensing
+
+__version__ = '9'

setup.py

@@ -1,8 +1,17 @@
 from setuptools import setup
 
+def read_version(path):
+    with open(path, 'rt') as f:
+        for line in f:
+            if line.startswith('__version__'):
+                return line.split("'")[1]
+        raise IOError
+
+version = read_version('rust2rpm/__init__.py')
+
 ARGS = dict(
     name="rust2rpm",
-    version="9",
+    version=version,
     description="Convert Rust crates to RPM",
     license="MIT",
     keywords="rust cargo rpm",