Add methods for determining the approx. (de)compressed size

[Quintus]

It looks as if liblzma has functions that estimate how large the uncompressed data of a compressed archive is, and how large a compressed archive of a given amount of uncompressed data is going to be. These should be made accessible by this binding.

[Quintus]

This turns out to be nontrivial as liblzma only provides internal APIs for this. See https://stackoverflow.com/questions/2171775/how-to-get-the-uncompressed-size-of-an-lzma2-file-xz-liblzma

Thus, this will not be implemented.