get CDF reference version correct
fix read bug
Tidy up 32/64-bit handling of CDF offsets and sizes.

The Buf interface now has a flag that can be re/set to change
control data values read by getOffset to be either 32 or 64 bit.
Previously it was done by wrapping the buffer, but in that case
it might not have got propagated to sub-buffers.
Adjusted compression to work with whole-file compression.

It wasn't clear from the docs that you need to prepend magic numbers
to the uncompressed stream to get the offsets to come out right.
Add Huffman encoding.
Perform end-of-stream handling in superclass
Add Adaptive Huffman decompression
Tidied up Compression class a bit
Fix some bugs and make some clarifications for non-existent records
Note improvements (incl. compression support) in implementation notes