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

doc/conf.py

@@ -15,7 +15,10 @@
 import sys
 import os
 on_rtd = os.getenv('READTHEDOCS') == 'True'
-from setuptools_scm import get_version
+if on_rtd:
+    import escpos
+else:
+    from setuptools_scm import get_version
 
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
@@ -70,10 +73,14 @@ copyright = u'2016, Manuel F Martinez and others'
 # |version| and |release|, also used in various other places throughout the
 # built documents.
 #
+if on_rtd:
+    # The full version, including alpha/beta/rc tags.
+    release = escpos.__version__
+else:
+    # locally setuptools_scm should work
+    release = get_version(root=root)
 # The short X.Y version.
-version = get_version(root=root)
-# The full version, including alpha/beta/rc tags.
-release = version
+version = '.'.join(release.split('.')[:2])  # The short X.Y version.
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.