Developer guidelines

A short document with development guidelines. First draft, but ready for some feedback.
I agree it's very subjective. Personally, I avoid abbreviations which aren't too long e.g. `input` to `inp` is not worth it for me.

But `initialization` to `init` might be worth it (10 characters!) as long as there is no ambiguity as to whether it should be `initialize`, `initialization`, `initial`, `initiate`, etc. In the case of `biases_init` I think it's pretty clear, so I wouldn't go out of my way to change it to `biases_initialization`. But I wouldn't write `init_bias` because it could be `initial_bias` as well as `initialize_bias`...