Developer guidelines

A short document with development guidelines. First draft, but ready for some feedback.
I agree with your treatment of this particular case with `biases_init`, but for me it shows that it is not an easy thing to decide on. In your original version `init` was an example of bad abbreviation, and now it turns out to be sometimes permissible.

My point is: let's keep the mandatory part of the style-guide unambiguous. `Variable names should be explanatory.` is sufficient, IMHO.