MS-DOS: Add Extended2 symbols to the bundled fonts

This change adds U+2299, U+2601 and U+2980 to the bundled fonts, so
that all symbols specified in the Extended2 symbol set are available.

Also, a few more directives are added to the files, so that FontForge
can load them and display their contents.

sys/msdos/fonts/nh-u20b.bdf

@@ -1,12 +1,21 @@
 STARTFONT 2.1
 FONTBOUNDINGBOX 10 20
-STARTPROPERTIES 3
+STARTPROPERTIES 8
 NOTICE "Additional characters to use with ter-u20b.bdf"
-COPYRIGHT "Copyright 2022 Ray Chason."
+COPYRIGHT "Copyright 2022, 2026 Ray Chason."
+NOTICE "Cloud glyph adapted from the uw-ptty0 font at"
+NOTICE "https://people.mpi-inf.mpg.de/~uwe/misc/uw-ttyp0/"
 NOTICE "NetHack may be freely redistributed.  See license for details."
+PIXEL_SIZE 20
+CHARSET_REGISTRY "ISO10646"
+CHARSET_ENCODING "1"
 ENDPROPERTIES
+CHARS 6
 STARTCHAR tripletilde
 ENCODING 8779
+SWIDTH 500 0
+DWIDTH 10 0
+BBX 10 20 0 -4
 BITMAP
 0000
 0000
@@ -29,8 +38,38 @@ BITMAP
 0000
 0000
 ENDCHAR
+STARTCHAR uni2299
+ENCODING 8857
+SWIDTH 556 0
+DWIDTH 10 0
+BBX 10 18 0 -3
+BITMAP
+0000
+0000
+0000
+0000
+0000
+0C00
+3F00
+6180
+4080
+CCC0
+CCC0
+4080
+6180
+3F00
+0C00
+0000
+0000
+0000
+0000
+0000
+ENDCHAR
 STARTCHAR uppereighth
 ENCODING 9620
+SWIDTH 556 0
+DWIDTH 10 0
+BBX 10 18 0 -3
 BITMAP
 FFC0
 FFC0
@@ -55,6 +94,9 @@ FFC0
 ENDCHAR
 STARTCHAR righteighth
 ENCODING 9621
+SWIDTH 556 0
+DWIDTH 10 0
+BBX 10 18 0 -3
 BITMAP
 0040
 0040
@@ -77,4 +119,58 @@ BITMAP
 0040
 0040
 ENDCHAR
+STARTCHAR uni2601
+ENCODING 9729
+SWIDTH 556 0
+DWIDTH 10 0
+BBX 10 18 0 -3
+BITMAP
+0000
+0000
+0000
+0000
+0000
+0000
+0780
+0FC0
+1CC0
+78C0
+E0C0
+C0C0
+FF80
+7F00
+0000
+0000
+0000
+0000
+0000
+0000
+ENDCHAR
+STARTCHAR uni2980
+ENCODING 10624
+SWIDTH 556 0
+DWIDTH 10 0
+BBX 10 18 0 -3
+BITMAP
+0000
+0000
+0000
+4900
+4900
+4900
+4900
+4900
+4900
+4900
+4900
+4900
+4900
+4900
+4900
+4900
+0000
+0000
+0000
+0000
+ENDCHAR
 ENDFONT