Add MANIFEST.in and setup.py

MANIFEST.in

+include Makefile
+include requirements.txt

setup.py

+#!/usr/bin/env python
+
+from setuptools import setup
+
+setup(
+    name='swh.core',
+    description='Software Heritage core utilities',
+    author='Software Heritage developers',
+    author_email='swh-devel@inria.fr',
+    url='https://forge.softwareheritage.org/diffusion/DCORE/',
+    packages=['swh.core', 'swh.core.tests'],
+    scripts=['bin/swh-hashdir', 'bin/swh-hashfile'],
+    install_requires=open('requirements.txt').read().splitlines(),
+    setup_requires=['vcversioner'],
+    vcversioner={},
+    include_package_data=True,
+)