Speed up the significant test

Hi,

Thanks for developing this wonderful tool for climate research.

I am using the following code to perform a significance test on wavelet coherence:
`scal_sig2 = scal.signif_test(method='ar1sim', number=1000)`
However, the process is extremely slow. I am wondering if it is possible to add a feature, such as parallel processing, to speed up the computation?

Best regards,
Cheng