more generic interface for solver

[pboesu]

The solver system is not open to extension in its current state:

  if(solver == 1 || solver == "ode"){
    #require(deSolve)
    out <- try(ode(inits, times, sim, parms=params, verbose=verbose , method=method, ...))
  }

Is there a reason why solver can't be made more generic? All it would really take is passing solver in as a function (along with a description of the form it should take). The existing ode/dde/dede if/else statements could be largely replaced by a little bit of wrapper code, such as:

if (is.character(solver)) {
  if (solver == "ode") {
    solver <- deSolve::ode(inits, times, sim, params, 
                           verbose=verbose, method=method, ...)
  } # ...and so on for the others.
}

In any case, because the method parameters passed along is the same as the default to ode, it can be dropped and passed along with ....

[pboesu]

postponed until https://github.com/pboesu/debinfer/milestone/2