libid3tag truncates strings on 64 bit systems

[Brian Havard]

In id3tag.h, the type id3_ucs4_t is typedef'd as an unsigned long. Clearly this type needs to be a 32 bit unsigned int but an unsigned long is 64 bit on a 64 bit system. Changing the typedef to read

typedef uint32_t id3_ucs4_t;

and #including <stdint.h> fixes the problem.

Without this fix, strings returned by id3_field_getstrings() are only ever 1 character long.