Removes ``lsqfit.BayesIntegrator`` (and ``BayesPDF``) which is replaced by the more capable ``vegas.PDFIntegrator`` in the ``vegas`` module (for multi-dimensional integration). Adds two new methods to ``nonlinear_fit``, for use with ``PDFIntegrator``: ``logpdf(p)`` and ``pdf(p)``.
Fixes for uncommon bugs when ``maxit=0`` or when using the ``noise`` parameter with no prior.