FITS header now includes whether the sampler has converged (MCCONVER), as reported by the supplied convergence function.
Refactored logic for generating FITS header information. _stats_as_header_cards now acts on a model rather than a trace database (so it has direct access to stochastic objects instead of just their trace names). Subclasses of ComponentBase now define their own translation tables for generating shortended trace names appropriate for FITS headers.