Remove explicit version specification

This commit removes the explicit listing of the version number in both
__init__.py and setup.py, and replaces the former with the version
number computed by setuptools_scm. As a prerequisite to that, I've added
a configuration item in pyproject.toml to have setuptools_scm write
the version number to a file.

I've imported the version number under the name `VERSION` to keep it
compatibile with previous versions of pytest_localserver. If `version`
is a more standard identifier, we might want to change or add that in
the future.

Author: diazona

pyproject.toml

@@ -1,3 +1,6 @@
 [build-system]
 requires = ["setuptools >=42", "setuptools_scm[toml] >=3.4.1", "wheel"]
 build-backend = "setuptools.build_meta"
+
+[tool.setuptools_scm]
+write_to = "pytest_localserver/_version.py"

pytest_localserver/__init__.py

@@ -1 +1 @@
-VERSION = '0.5.1.post0'
+from pytest_localserver._version import version as VERSION

setup.py

@@ -2,20 +2,12 @@
 import sys
 
 
-VERSION = '0.5.1.post0'
-
-
 def read(fname):
     # makes sure that setup can be executed from a different location
     import os.path
     _here = os.path.abspath(os.path.dirname(__file__))
     return open(os.path.join(_here, fname)).read()
 
-# make sure that versions match before uploading anything to the cheeseshop
-if 'upload' in sys.argv or 'register' in sys.argv:
-    import pytest_localserver
-    assert pytest_localserver.VERSION == VERSION
-
 
 class PyTest(Command):
     user_options = []
@@ -30,7 +22,6 @@ def run(self):
 
 setup(
     name='pytest-localserver',
-    version=VERSION,
     author='Sebastian Rahlf',
     author_email='basti@redtoad.de',
     maintainer='David Zaslavsky',