Introduce the revised coding style.

Opinion time!

I did a general revising of the coding style, since the one on the wiki is quite old. Also this will put it in a file within the repo, which is good because whenever someone makes a pull request it will have a little notification that tells people to make sure that they've read the guidelines (see [here](https://github.com/blog/1184-contributing-guidelines) for more on that). Having it in the repo will be much easier for potential contributors to see instead of the wiki.

This is the first 'draft' so I strongly encourage people to give me opinions and suggestions on this until we agree upon things. 
I disagree. When reading source code that I'm not familiar with, a variable prefix of s_ (in theory) tells me that they are only used in this particular file - which is important to understand to grasp how things are working together, because if it was a global I'd have to look up all other occurrences of that variable to figure out how it's being used. Hence, removing the distinction between globals and statics hence makes it harder for new developers to understand the code base IMO.