Include license file in the generated wheel package

The wheel package format supports including the license file. This is
done using the [metadata] section in the setup.cfg file. For additional
information on this feature, see:

https://wheel.readthedocs.io/en/stable/index.html#including-the-license-in-the-generated-wheel-file

Distributing the wheel now complies with the license:

> The above copyright notice and this permission notice shall be
> included in all copies or substantial portions of the Software.

setup.cfg

@@ -27,3 +27,5 @@
 #library_dirs=../../../libyaml/tags/0.1.4/win32/vs2008/output/release/lib
 #define=YAML_DECLARE_STATIC
 
+[metadata]
+license_file = LICENSE