tendril bounds objects

[ethanrublee]

implement a way for specifying the min,max values of a tendril.

Also maybe a validator (think regex validation for strings).

The goal being that this might be a good way to construct parameter tuning guis.

[ethanrublee]

Idea for client syntax

bool validate(std::string x)
{
  return x.size() < 32;
}
void declare_params(tendrils& params)
{
  params.declare<double>("x","x is a parameter", 0)( min_(-20.0) )( max_(100.0) );
  params.declare<std::string>("str","i'm a string!","foo")(validate);
}

[ethanrublee]

Holding off on this for now.