Change project name to Thun.

I waited too long to upload to PyPI and some other bastard snagged the name.  I originally wanted to call it "Thun" as a tribute to Manfred von Thun, but I was concerned that this might seem to violate the thrid clause in the license of the original Joy code, to wit:

3. The name of the author may not be used to endorse or promote products  derived from this software without specific prior written permission.

Since the author is deceased I don't know of whom to ask permission to call this project Thun, but since I am not trying to "endorse or promote" this project with his name it should be alright.  In any event if anyone complains I can rename the project again.

joy/joy.py

@@ -14,20 +14,20 @@ original version(s) written in C.  A Tkinter GUI is provided as well.
 
     Copyright © 2014, 2016, 2017 Simon Forman
 
-    This file is part of Joypy.
+    This file is part of Thun.
 
-    Joypy is free software: you can redistribute it and/or modify
+    Thun is free software: you can redistribute it and/or modify
     it under the terms of the GNU General Public License as published by
     the Free Software Foundation, either version 3 of the License, or
     (at your option) any later version.
 
-    Joypy is distributed in the hope that it will be useful,
+    Thun is distributed in the hope that it will be useful,
     but WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
     GNU General Public License for more details.
 
     You should have received a copy of the GNU General Public License
-    along with Joypy.  If not see <http://www.gnu.org/licenses/>.
+    along with Thun.  If not see <http://www.gnu.org/licenses/>.
 
 
 § joy()