Curses: implement the windowcolors option

Allow changing the curses windows foreground and background colors,
for example:

OPTIONS=windowcolor:menu #8000F0/20F080 message grey/blue

doc/Guidebook.mn

@@ -4996,7 +4996,7 @@ plus widen each inventory line by two columns.
 .lp windowcolors
 If NetHack can, it should display windows with the specified
 foreground/background colors.
-Windows GUI only.
+Windows GUI and curses windowport only.
 The format is
 .si
 .lp "OPTION=windowcolors:wintype foreground/background"

doc/Guidebook.tex

@@ -5513,7 +5513,7 @@ plus widen each inventory line by two columns.
 \item[\ib{windowcolors}]
 If {\it NetHack\/} can, it should display windows with the specified
 foreground/background colors.
-Windows GUI only.
+Windows GUI and curses windowport only.
 The format is
 \begin{verbatim}
     OPTION=windowcolors:wintype foreground/background

doc/fixes3-7-0.txt

@@ -2539,6 +2539,7 @@ curses: if panictrace is triggered, reset the terminal before giving backtrace
 curses: if a message is marked urgent, override message suppression initiated
 	by user having typed ESC at previous More>> prompt
 curses: implement a dialog for the windowborders option
+curses: implement the windowcolors option
 Qt: the "paper doll" inventory subset can be controlled via the "Qt Settings"
 	dialog box ("Preferences..." on macOS)
 Qt: draw a border around each tile in the paper doll inventory; when BUC is