Adding promises to coding standards

I've added to the Coding standard and want you all to take a look and make sure you're happy with the changes before merging to master.
@kevinhodges 
@philmeehan 
@nithyavinod 
@robhuzzey 
@panicnot 
@david-hersey 
@MCooke 
@lukefrake 
@nickine 
@hpoom 

Fair one! Agreed!