add Python packaging

.gitignore

 __pycache__/
+/build/
+/dist/
 *~

MANIFEST.in

+include *.rst
+include test_*.py

README.rst

+Kwant-Spectrum is an extension to `Kwant <http://kwant-project.org/>`_ that
+adaptively analyzes band structures of infinite quasi-1d systems.  The
+bandstructure is approximated to an arbitrary precision by piecewise cubic
+polynomials.  Functionality to deal with special points, intervals, and the
+periodic nature of the spectrum is provided.
+
+`Full documentation including a tutorial
+<https://kwant-project.org/extensions/spectrum/>`_ is available .  Report bugs
+and follow development through the `Kwant-Spectrum repository
+<https://gitlab.kwant-project.org/kwant/spectrum>`_.

setup.py

+#!/usr/bin/env python3
+
+from setuptools import setup
+
+# Get the long description from the README file.
+with open('README.rst', encoding='utf-8') as f:
+    long_description = f.read()
+
+setup(
+    name='kwant-spectrum',
+    version='0.0',
+    description='Adaptive band structure analyzer for Kwant leads',
+    long_description=long_description,
+    long_description_content_type='text/x-rst',
+    url='https://gitlab.kwant-project.org/kwant/spectrum',
+    author='T. Kloss, C. W. Groth, X. Waintal, et al.',
+    author_email='kloss@itp.uni-frankfurt.de',
+    classifiers=[
+        'Development Status :: 4 - Beta',
+        'Intended Audience :: Science/Research',
+        'Intended Audience :: Developers',
+        'Topic :: Software Development',
+        'Topic :: Scientific/Engineering',
+        'License :: OSI Approved :: BSD License',
+        'Programming Language :: Python :: 3 :: Only',
+    ],
+    keywords='physics kwant bandstructure',
+    py_modules=["kwant_spectrum"],
+    python_requires='>=3.5',
+    install_requires=['kwant >= 1.4'],
+    extras_require={'test': ['pytest'],},
+)