Long-distance matching beyond 2 GiB

**Is your feature request related to a problem? Please describe.**
The highest window size specifiable is `--memory=2048M`. , even though modern computers have more memory at their disposal.

**Describe the solution you'd like**
I suggest allowing any window size supported by a computer.

**Describe alternatives you've considered**
There is already `lrzip`, but looking at its changelog, new versions frequently break compatibilitiy with existing versions. I hope that when zst implements window size limits beyond 2048M, the first version to support it will at least be able to read from archives created in future versions.