rewrite/discuss coding guidelines

[cebe]

I think we should rewrite/discuss our coding guidelines.
After this discussion with @creocoder I thought about the E prefix and came to the conclusion that I'd miss it.

I think the E prefix was quite a good thing to mark extension classes as just that, extensions and not part of my project.
So why do we need that? Not really for class name conflicts but for having a scope.
Yii core classes have the C, extensions the E and my own projects classes are without prefix.
This is what I do when extending yii core classes: create a class with the same name but without the C prefix. Same thing could be done with yiiext extensions when they have the E prefix. If the extension I want to use does not fit all my needs exactly (which is the common case I think) I can extend it the same way I extend yii core classes.

btw: guidelines should also appear on yiiext.github.com