Add suport for "standard" NO_COLOR env variable

See https://no-color.org

nnn.1

@@ -410,6 +410,8 @@ separated by \fI;\fR:
 .Pp
 \fBnnn:\fR this is a special variable set to the hovered entry before executing
 a command from the command prompt or spawning a shell.
+.Pp
+\fBNO_COLOR:\fR if defined, disable ANSI color output.
 .Sh KNOWN ISSUES
 .Nm
 may not handle keypresses correctly when used with tmux (see issue #104 for

src/nnn.c

@@ -6867,6 +6867,9 @@ int main(int argc, char *argv[])
 		}
 	}
 
+	if (getenv("NO_COLOR"))
+		g_states |= STATE_NOCOLOR;
+
 #ifdef DBGMODE
 	enabledbg();
 	DPRINTF_S(VERSION);