CRAN release v2.0.0

NEW FEATURES

• Two new built-in models: 'SISe_sp' and 'SISe3_sp' with spatial
  coupling.
• Added the 'run_outer' method to run a model on scaled 'gdata'
  parameters.

IMPROVEMENTS

• Added two synthetic datasets 'u0_SISe3' and 'events_SISe3' to
  demonstrate how to use SimInf.
• Several improvements to the documentation.
• Added summary method to the siminf_model class and the
  scheduled_events class.

CHANGES

• The slot N in scheduled_events is changed from dgCMatrix to matrix.
• Refactoring of the 'show' method for the siminf_model class and the
  scheduled_events class.
• Renamed function prototype 'PostTimeStepFun' to 'PTSFun' and
  'PropensityFun' to 'TRFun'.
• Renamed 'init' argument to 'u0' in the 'SISe' and 'SISe3' methods.
• Changed 'node', 'dest', 'select' and 'shift' to one-based indices in
  'scheduled_events'.

BUG FIXES

• Changed to use 'gsl_rng_uniform_pos' instead of 'gsl_rng_uniform' to
  avoid 0 in the direct SSA. If zero was randomly selected and the
  first compartment empty, the simulator could enter a negative state.