Add entry point

[oesteban]

This PR:

• Adds a new entry point. This way, installing Spearmint creates a new executable file called spearmint. To execute the experiments, you can issue spearmint --config config.json path/to/experiment wherever you want to get the outputs in your system.
• Added entry in .gitignore so that python setup.py develop can be used to deploy spearmint in development environments.

I hereby declare that I agree with the contribution agreement (permanent link: https://github.com/HIPS/Spearmint/blob/e719c56cee9eefda5df6af40f834c9fa310e23a5/CONTRIBUTING.rst)