Move `ws_deque` to lockfree

[kayceesrk]

The work-stealing deque in domainslib [1] seems useful to have outside of domainslib. We should perhaps move this to ocaml-multicore/lockfree and make domainslib depend on lockfree?

Also, I'd archive the current lockfree library and start afresh since the current implementation predates the OCaml memory model [2].

[1] https://github.com/ocaml-multicore/domainslib/blob/master/lib/ws_deque.ml
[2] https://kcsrk.info/papers/pldi18-memory.pdf

[jmid]

This is addressed with the release of lockfree 0.2.0 and #70