Gave each file its own copyright/license notice.

This is the normal way to do things. I don't think trying to contain all of this information in one file is worth it.

I considered going through each file, looking through the commit histories, and seeing what all of the copyright holders are, but doing this for 274 files myself would be too much. I've decided to leave it up to each contributor to handle their own copyright notices, instead, except for a couple of files that didn't point you to naev.h previously, where I indicated the person responsible for starting the respective file.