Sort comes pretty much automatically, as no script relies on the
undefined behaviour of the input _not_ being sorted, we might as well
sort the sorted input already.
The only downside is memory usage, which can be an issue for large
files.
The o-flag was trivial to implement.
Options that are specific to a single key definition are not
supported (e.g. "sort -k 2,3n -k 4,4"). Should you try to specify
such definitions, sort will return with EXIT_FAILURE and an error
message. Instead, all key definitions exclusively use the global
settings.
It always behaves like -b was set.
