TO-DO LIST

* write pompCBuilder support for 'onestep.dens' and 'gillespie.sim' plugins.

* effects of replacing 'sample.int' with systematic resampling inside 'bsmc'

* parameter transformations: put 'transform' option into each estimation routine
  (spect.match)

* unit tests for 'sannbox'

* Improve 'pmcmc' to take advantage of all particles.

* Partial rejection control for 'pfilter'?

* Adaptive particle numbers in pfilter.

* Write 'plot' and 'print' methods for 'pfilterd.pomp' objects.  
  Would this display effective sample size, conditional log likelihood, filter means, prediction variances, prediction means?

* Add plugin for adaptive tau leaping algorithm.

* Parallel 'pfilter' algorithm.

* Add LPA model examples.

* SDE examples.

* Extended Kalman filter.

* Plugin for compartmental models.
