Add links to the font specifications.

Add links to specifications for the Type1, CFF, and TrueType font file
formats, provided by Adrian Johnson.

src/cairo-cff-subset.c

@@ -34,6 +34,11 @@
  *      Eugeniy Meshcheryakov <eugen@debian.org>
  */
 
+/*
+ * Useful links:
+ * http://www.adobe.com/devnet/font/pdfs/5176.CFF.pdf
+ */
+
 #define _BSD_SOURCE /* for snprintf(), strdup() */
 #include "cairoint.h"
 #include "cairo-scaled-font-subsets-private.h"

src/cairo-truetype-subset.c

@@ -34,6 +34,12 @@
  *	Adrian Johnson <ajohnson@redneon.com>
  */
 
+/*
+ * Useful links:
+ * http://developer.apple.com/textfonts/TTRefMan/RM06/Chap6.html
+ * http://www.microsoft.com/typography/specs/default.htm
+ */
+
 #define _BSD_SOURCE /* for snprintf(), strdup() */
 #include "cairoint.h"
 

src/cairo-type1-subset.c

@@ -33,6 +33,11 @@
  *	Kristian Høgsberg <krh@redhat.com>
  */
 
+/*
+ * Useful links:
+ * http://partners.adobe.com/public/developer/en/font/T1_SPEC.PDF
+ */
+
 #define _BSD_SOURCE /* for snprintf(), strdup() */
 #include "cairoint.h"
 #include "cairo-type1-private.h"