Re-formatted code according to style guides.

Code was re-formatted according to style guide, in particular 120
maximum character width with 4-space indentation.

Eclipse formatter configuration was also added.
Added contributors guide.

Added developer's contributors guide to the project documentation as described
here:

https://github.com/blog/1184-contributing-guidelines

This includes clear instructions on how to submit pull requests and bug
reports. Also defines the Eclipse Formatter code style guide.