Move __version__ into __init__.py

A little bit of clean parsing code in setup.py and the enforcement
from `black`, and it becomes possible to ditch a file which only held
a single value. Similarly update the version parsing in the makefile.

Makefile

@@ -1,6 +1,6 @@
 .PHONY: lint test docs build release clean
 
-NOSE2_VERSION=$(shell grep '^__version__' nose2/_version.py | cut -d '"' -f2)
+NOSE2_VERSION=$(shell grep '^__version__' nose2/__init__.py | cut -d '"' -f2)
 
 lint:
 	tox -e lint

nose2/__init__.py

@@ -1,4 +1,5 @@
-from nose2._version import __version__
 from nose2.main import discover, main
 
+__version__ = "0.12.0"
+
 __all__ = ("__version__", "discover", "main")

setup.py

@@ -1,8 +1,19 @@
 import os
+import re
 
 from setuptools import find_packages, setup
 
-VERSION = open("nose2/_version.py").readlines()[-1].split()[-1].strip("\"'")
+
+def read_version(filename):
+    # use of " over ' will be enforced by "black"
+    version_pattern = re.compile(r'__version__ = "([^"]*)"')
+    with open(filename) as fp:
+        for line in fp:
+            m = version_pattern.match(line)
+            if m:
+                return m.group(1)
+    raise Exception("could not parse version from {}".format(filename))
+
 
 MAINTAINER = "Stephen Rosen"
 MAINTAINER_EMAIL = "[email protected]"
@@ -11,7 +22,7 @@
 
 setup(
     name="nose2",
-    version=VERSION,
+    version=read_version("nose2/__init__.py"),
     packages=find_packages(),
     extras_require={
         "coverage_plugin": ["coverage"],