Fix location of RELEASE-VERSION file for getting the omego version

- Save the RELEASE-VERSION file under omego/ directory
- Accordingly fix MANIFEST.in and setup.py
Add version command to retrieve the current version of omego
Use setuptools rather than distutils.core

This should produce the omego entry point under bin/
Merge pull request #15 from sbesson/version_fix

Fix omego version packaging and add version command