added Stuffit Support

The extraction tool can be found at
   -http://my.smithmicro.com/downloads/files/stuffit520.611linux-i386.tar.gz
Merge pull request #87 from ddcc/master

Update header for TRX to include versioning and offsets
Added back trx validation checks
Fixed CramFS signature bugs
Merge pull request #89 from ssem/master

added Stuffit Support
Updated stuffit signatures
Updated install docs to include unstuff
Fix bug with unsigned values appearing as negative signed values