fixes issue ulikunitz#40

Release v0.5.9

Release v0.5.8: fixes security issue ulikunitz#35

Fixes issue ulikunitz#27

This release includes a go.mod file. Many thanks to

[M. J. Fromberger](https://github.com/creachadair) for providing the fix.

v0.5.5: fixes issue ulikunitz#19

Release 0.5.4

Fixes issue ulikunitz#15.

Release v0.5.3 fixes issue ulikunitz#12 for empty xz streams.

Release v0.5.2

Release v0.5.2 fixes an issue with xz block header padding.

Release v0.5.1 fixing an issue on the 32-bit platform.