Support for "r" & "R" parser/format types

[dbrxnds]

Hi,

We've been using this library recently and it has been working great, however, we've run into a case that this lib does not (yet?) seem to cover. As found here, PHP serialization has the possibility of containing r (reference) and R (pointer reference) format types. Is there a specific reason to that this is not supported? Could this be supported?

We've also created a small Codesandbox to reproduce the issue: https://codesandbox.io/s/bold-vaughan-5jdetr?file=/src/index.js

Our current solution is to use phpunserialize, same as in the codesandbox. But that package is very outdated and doesn't support TS, so we would prefer to stay with this one.

[steelbrain]

I would be happy to accept a PR for this