BUGS/ISSUES:

  calling profile, etc. on mle objects
created inside a function doesn't work

  should print warning immediately if convergence fails

TO DO:

more documentation -- especially S4 methods!
catch/interpret more error messages?
  (try to filter last.warning?)


WISHLIST:
analytic derivatives
relist
subset
predict (feasible for formula arguments
          if we know the MEAN of the relevant distribution?)

document argument handling:

  start must be a named vector or a named list
       [OR?? inherit from parnames(minuslogl)?]
  if start is not a list (i.e. a numeric vector)
  set vecpar TRUE
  convert start to a list

  if missing and default.start is TRUE use formals(minuslogl)