Minor spec

Added guard bytes
Narrowed compressionType
Added TPUID copy constructor, fixed toString() format
Added getEntry() and syncCount()

Also guard bytes constant 'INDX' 0x494E4458
Added getCompressionId() to AssetHandles, rename AssetHandle implementations
Refactoring for rename, also setting compressionId
IndexEntry - Sha256 is 32 bytes, not 16
Fixed NullPointer in copy constructor, also create new with version
More guard bytes
Header sizeOf and toString
Update Reader to match spec, also removed hardcoded version
Added Writer and a MemoryPacBuilder to create files
Initial set of test cases