API for getting model parameters information

Is it possible to get the information about the stanfit object parameters in Rstan?
E.g. get_pars_info(stanfit) that would return something like:

list( a = c( type = 'vector', dim = 2, lower = -1, upper = 1 ),
      b = c( type = 'matrix', dim = c( 2, 5 ), lower = 0, upper = NA ) )

One potential use-case. I've ended up using DEoptim R package to optimize the function defined as a Stan model (log_prob(stanfit, upars)). DEoptim allows specifying element-wise constraints on the parameter vector, and it appears that differential evolution in the constrained space is much more efficient than in the unconstrained one. ATM I have to "manually" take care that constraints specification for DEoptim is in sync with the
Stan model, with get_pars_info() it would be possible to generate this specification automatically.

Start by inspecting the stanfit object and the log_prob(stanfit, upars) interface mentioned in the issue to determine what parameter metadata is available. Done means providing a get_pars_info(stanfit)-style API that returns parameter types, dimensions, and bounds in a form usable for element-wise constraints.