Feature Request (?): support for cdf or log_cdf in the mixture family

[jhn-nt]

I am currently working with mixtures and have been trying the "MixtureOfTwo" class. When I try to compute the cumulative distribution function, however, I am met with the non-implemented error: "NotImplementedError: Distribution MixtureOfTwo does not implement log_cdf"

Will log_cdf be implemented at some point?

Thank you very much and thank you for developing this fantastic project

Giovanni