Improve versioning

km3io/__init__.py

+from .__version__ import version
+__version__ = version
+
 from .aanet import AanetReader
 from .jpp import JppReader

km3io/__version__.py

+#!/usr/bin/env python
+# Filename: __version__.py
+# pylint: disable=C0103
+"""
+Pep 386 compliant version info.
+
+    (major, minor, micro, alpha/beta/rc/final, #)
+    (1, 1, 2, 'alpha', 0) => "1.1.2.dev"
+    (1, 2, 0, 'beta', 2) => "1.2b2"
+
+"""
+from __future__ import absolute_import, print_function, division
+
+from os.path import dirname, realpath, join
+
+from setuptools_scm import get_version
+
+version = 'unknown version'
+
+try:
+    version = get_version(root='..', relative_to=__file__)
+except LookupError:
+    with open(join(realpath(dirname(__file__)), "version.txt"), 'r') as fobj:
+        version = fobj.read()

requirements.txt

 uproot>=3.10.12
+setuptools_scm