Signed-off-by: NPhillip Lougher <phillip@lougher.demon.co.uk>

This adds a decompressor framework which allows multiple compression
algorithms to be cleanly supported.

Also update zlib wrapper and other code to use the new framework.
Signed-off-by: NPhillip Lougher <phillip@lougher.demon.co.uk>

Move zlib buffer init/destroy code into separate wrapper file.  Also
make zlib z_stream field a void * removing the need to include zlib.h
for most files.
Signed-off-by: NPhillip Lougher <phillip@lougher.demon.co.uk>

Signed-off-by: NPhillip Lougher <phillip@lougher.demon.co.uk>