Log Message:
Changes 5.0.0:
* The memory usage limit is now disabled by default.
* Added support for XZ_DEFAULTS environment variable.
* The compression settings associated with the preset levels
  -0 ... -9 have been changed. --extreme was changed a little too.
* If a preset level (-0 ... -9) is specified after a custom filter
  chain options have been used (e.g. --lzma2), the custom filter
  chain will be forgotten. Earlier the preset options were
  completely ignored after custom filter chain options had been seen.
* xz will create sparse files when decompressing if the uncompressed
  data contains long sequences of binary zeros.
* Support for "xz --list" was added. Combine with --verbose or
  --verbose --verbose (-vv) for detailed output.
* I had hoped that liblzma API would have been stable after
  4.999.9beta, but there have been a couple of changes in the
  advanced features, which don't affect most applications:
  - Index handling code was revised. If you were using the old
    API, you will get a compiler error (so it's easy to notice).
  - A subtle but important change was made to the Block handling
    API. lzma_block.version has to be initialized even for
    lzma_block_header_decode(). Code that doesn't do it will work
    for now, but might break in the future, which makes this API
    change easy to miss.
* The major soname has been bumped to 5.0.0. liblzma API and ABI
  are now stable, so the need to recompile programs linking against
  liblzma shouldn't arise soon.