add version-strings into the module

The version string is in the module as __version__ available.
In the doc the version will be automatically parsed. The version comes
from the installed module if on read the docs or directly from
setuptools_scm if you are working locally.
The CLI will issue the version string if you call it with the option
'version'. The CLI does not accept commands like '--version', since this
would not be conform with the rest of the interface (and argparse).

The configuration for loading the version-string is adapted from
pimutils/vdirsyncer. It autogenerates a version string setuptools_scm at
install-time and then adds it to the __version__ member in __init__.py

I adapted the GitHub-template with a fitting comment and bumped the
changelog.

closes #141

setup.py

@@ -45,9 +45,24 @@ class Tox(test_command):
         errno = tox.cmdline(args=args)
         sys.exit(errno)
 
+
+setuptools_scm_template = """\
+# coding: utf-8
+# file generated by setuptools_scm
+# don't change, don't track in version control
+from __future__ import unicode_literals
+
+version = '{version}'
+
+"""
+
+
 setup(
     name='python-escpos',
-    use_scm_version=True,
+    use_scm_version={
+        'write_to': 'src/escpos/version.py',
+        'write_to_template': setuptools_scm_template,
+    },
     url='https://github.com/python-escpos/python-escpos',
     download_url='https://github.com/python-escpos/python-escpos/archive/master.zip',
     description='Python library to manipulate ESC/POS Printers',