[libredwg] Copyright assignments and notices

[Rodrigo Rodrigues da Silva]

Thien and Till, IIRC you have sent the form with your personal data for
the copyright assignment to address@hidden Please confirm
that. If you haven't, please do it. BTW, if you have sent the form,
have you received a letter from the FSF? You should sign it and send it
back to the FSF.

Felipe(s) and I have signed the papers. I have changed all file
headers to reflect this, keeping (C) FSF and then the authorship below. 

I have also made copyright notices for Thien and Till while you don't
have the paperwork done (I'll do the possible to get it done soon
and change the headers).