update license and credits

LICENSE

@@ -1,5 +1,5 @@
 Million Perfect Letters
-(c) 2020 by 4am
+Copyright (c) 2020, 4am
 
 Due to the inclusion of several GPL-licensed libraries (see below), the program
 as a whole is licensed under the GPL 3.0 or later. However, all of my original
@@ -31,8 +31,45 @@ CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
                                        ~
 
 
+Courier Double Prime
+Copyright (c) 2019-2020, 4am
+with Reserved Font Name "Courier Double Prime"
+
+This font is licensed under the SIL Open Font License, Version 1.1. See
+"res/Courier Double Prime/OFL.txt" for the full license text.
+
+It is a derivative work, a mostly faithful conversion of Courier Prime to the
+Apple ][ hi-res graphics screen.
+
+Courier Prime
+Copyright (c) 2015, Quote-Unquote Apps (http://quoteunquoteapps.com)
+with Reserved Font Name "Courier Prime"
+
+Courier Prime was designed by Alan Dague-Greene for John August and
+Quote-Unquote Apps. Courier Prime is licensed under the SIL Open Font License,
+Version 1.1.
+https://quoteunquoteapps.com/courierprime/
+
+
+
+                                       ~
+
+
+Heavy Silk
+Copyright (c) 2020, 4am
+with Reserved Font Name "Heavy Silk"
+
+This font is licensed under the SIL Open Font License, Version 1.1. It is an
+original work; it is not based on any other font.
+
+See "res/Heavy Silk/OFL.txt" for the full license text.
+
+
+                                       ~
+
+
 Electric Duet player
-Copyright (C) 1979-2015 by Paul Lutus
+Copyright (c) 1979-2015, Paul Lutus
 http://arachnoid.com/administration
 
 This program is free software; you can redistribute it and/or modify it under
@@ -48,12 +85,14 @@ You should have received a copy of the GNU General Public License along with
 this program; if not, write to the Free Software Foundation, Inc.,
 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 
+See "res/gpl-2.0.txt" for the full license text.
+
 
                                        ~
 
 
 MockingDuet player
-Copyrighth (C) 2017 by cybernesto
+Copyright (c) 2017, cybernesto
 
 This program 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
@@ -67,12 +106,15 @@ 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
 this program. If not, see <http://www.gnu.org/licenses/>.
 
+See "res/gpl-3.0.txt" for the full license text.
+
 
                                        ~
 
 
-The main menu music is "Cembalo", written by Aliam Lenat in 2012 and released to
-the public domain. I downloaded it (sheet music as a PDF, plus a sample MIDI
-file) from <https://www.free-scores.com/download-sheet-music.php?pdf=49126> and
-converted it to the Electric Duet file format. My conversion is also released
-to the public domain.
+The main menu music is "Sicilienne" by Gabriel Fauré. I downloaded it from
+https://www.mutopiaproject.org/ftp/FaureG/O78/faure-sicilienne-guitare-doigtee/
+faure-sicilienne-guitare-doigtee-a4.pdf and converted it to the Electric Duet
+file format. My conversion is released to the public domain.
+
+See "res/Sicilienne score.zip" for the original score as a PDF.