Multi-threaded stemming?

First of all, thank you for the library!

I was wondering is it possible to use it with multi-threading?

I've tried initializing several stemmers (`Stemmer()`), one for each thread, but it led to a segfault. I
'm not sure why - I thought it should have initialized separate stemmers.

Is there another workaround that can use to parallelize the stemming workload?

No source file or test is named. Start by reproducing the reported segfault with one Stemmer() per thread and inspect the stemmer initialization and threaded execution paths. Done means parallel stemming works without a segfault, or the supported limitation and a safe workaround are documented.

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