adds an unSynch function that converts the frameLength bytestream from a synch-safe integer. Required for id3v2.4 parsing
updating the tone16bit_id3v2.4.mp3 sample. I have embedded an APIC, this previously caused 'panic: value method taggolib.mp3Parser.Encoder called using nil *mp3Parser pointer' during test execution.
Merge pull request #4 from jesseward/id3v2-unsynch-frame

Unsynchronization of id3v2 frameLength integers