Pretty: add the ability to stream out to a generic thing

Instead of always requiring FILE *. This does mean a slight code size
increase, since we now have to pass an extra parameter down the function
stack, plus we're making indirect calls, but it's worth it.

Signed-off-by: Thiago Macieira <thiago.macieira@intel.com>

Author: thiagomacieira

src/cbor.h

@@ -591,6 +591,13 @@ enum CborPrettyFlags {
     CborPrettyDefaultFlags          = CborPrettyIndicateIndetermineLength
 };
 
+typedef CborError (*CborStreamFunction)(void *token, const char *fmt, ...)
+#ifdef __GNUC__
+    __attribute__((__format__(printf, 2, 3)))
+#endif
+;
+
+CBOR_API CborError cbor_value_to_pretty_stream(CborStreamFunction streamFunction, void *token, CborValue *value, int flags);
 CBOR_API CborError cbor_value_to_pretty_advance_flags(FILE *out, CborValue *value, int flags);
 CBOR_API CborError cbor_value_to_pretty_advance(FILE *out, CborValue *value);
 CBOR_INLINE_API CborError cbor_value_to_pretty(FILE *out, const CborValue *value)