Add documentation and tidy code.

No logic changes.

First commit moves README.developers to CONTRIBUTING - github automatically detects this file. Also adds notes on guideline for contributing and what is acceptable.

Since the first commit established a conservative coding standard, I tidied the code in accordance with what I gathered was the standard by observing the existing code. However I was conservative here and limited tidy this to only indentation. Exact script used was `perltidy -nola -tabs -l 80 -io *.pl`.