Add support for \s escapes to qfcc.

I guess \s is an fteqcc extention for toggling bold characters. At the
request of freewill.

tools/qfcc/doc/man/qfcc.1

@@ -493,6 +493,8 @@ Formfeed character (not in quake engines). Equivalent to \(rsx0c.
 .B \(rsr
 Carriage return. Equivalent to \(rsx0d.
 .TP
+.B \(rss
+Toggle "bold" characters (add 0x80).
 .B \(rst
 Tab character. Equivalent to \(rsx09.
 .TP

tools/qfcc/source/strpool.c

@@ -240,6 +240,9 @@ make_string (char *token, char **end)
 				case 'r':
 					c = '\r';
 					break;
+				case 's':
+					mask ^= 0x80;
+					break;
 				case 't':
 					c = '\t';
 					break;