v5.5.1alpha
tuklib_integer: Fix typo discovered by codespell.
Bump version number for 5.5.1alpha.
xz, xzdec, lzmainfo: Use tuklib_attr_noreturn.
Scripts: Change quoting style from `...' to '...'.
xz: Use threaded mode by defaut (as if --threads=0 was used).
xz: Update website URLs in the man pages.
Build: Prepare to support Automake's subdir-objects.