MDS smacof n_jobs argument

[choltz95]

Hi- I just noticed that even though embed_mds accepts an n_jobs argument, it never gets passed to the smacof wrapper ~defaulting to 1 each time.

Is that a problem? Btw, unrelated, but sklearn also has a parallel pdist which also takes an n_jobs argument.

[scottgigante]

@choltz95 this is likely an oversight. It shouldn't be terribly impactful assuming you are using n_landmark=2000 but worth fixing nonetheless. I am no longer an admin on this repo but I'd encourage you to submit a PR.