Add converged status to harmony object

[potulabe]

Thank you very much for this port!
What do you think about adding a "converged" state to Harmony object properties? (https://github.com/slowkow/harmonypy/blob/master/harmonypy/harmony.py#L242)
It would be easier to check it programmatically rather than reading logs.

[potulabe]

Although one can just call ho.check_convergence(1), so maybe it's useless :)