Bug#516351: copyright and license refinement

[MK <halfcountplus@intergate.com>]

At the request/recommendation of someone at "Savannah" I have added 
some more explicit copyright and licensing info, qv.

https://savannah.gnu.org/task/?9211

The code remains the same so I have not incremented the version.  The 
tarballs via
www.intergate.com/~halfcountplus/see/
seetxt.sourceforge.net
reflect this; I have to wait to update the tarball accessed thru the 
sourceforge project page (https://sourceforge.net/projects/seetxt/).

This includes a COPYRIGHT section added to the man page, but legally 
speaking everything remains the same so the issue is Not Very 
Significant.

Have a nice weekend!