Accept rational-precision mixed profiles for logit_estimate

[rahulsavani]

Requested enahancement or feature

At the moment liap_solve expects the strategy profile passed to be of float (double) precision (MixedStrategyProfileDouble). It would be good to allow a rational-precision profile too, converting it to a double profile internally within the solver function call.

This is completely analogous to issue #458 which is for logit_estimate.