Construct. level is the same as for D.zlib.compress().
A destructor is present on this object, but not explicitly documented in the source.
Compress the data in buf and return the compressed data. The buffers returned from successive calls to this should be concatenated together.
Compress and return any remaining data. The returned data should be appended to that returned by compress().
Used when the data to be compressed is not all in one buffer.