expose main launcher in package too

This unbreaks the setuptools entry point since it wants to call
`yamlreader.__main` and not `yamlreader.yamlreader.__main`

This resolves #9

src/main/python/yamlreader/__init__.py

@@ -2,6 +2,6 @@
 
 from __future__ import print_function, absolute_import, unicode_literals, division
 
-from .yamlreader import data_merge, yaml_load, YamlReaderError
+from .yamlreader import data_merge, yaml_load, YamlReaderError, __main
 
-__all__ = ['data_merge', 'yaml_load', 'YamlReaderError']
+__all__ = ['data_merge', 'yaml_load', 'YamlReaderError', '__main']