Authors/Thanks files

[Tim Rice]

Hey all,

I was looking for low-hanging fruit to try out my first git push to the 
datamash repo, and noticed AUTHORS and THANKS were a bit sparse. So, I've added 
a list of everyone who I could find in past commit messages. Let me know if I 
missed someone (or if you want your name removed.)

Furthermore, these two files were unnecessarily encumbered by copyright 
headers. Most jurisdictions have the default position that authorship 
automatically confers copyright. Then, since all authorship information is in 
the Git history, an extra copyright header is redundant.

Removing such formality is consistent with what we see in other GNU projects 
like Sed and Tar. Those projects simply list contributors, without belaboring 
copyright in AUTHORS and THANKS.

Still, if you have a good reason why you think "Copyright (C) this and that" 
should remain at the top of AUTHORS and THANKS, let me know.

Cheers,

Tim