rng configuration object

[richfitz]

Now that we have multiple algorithms possible, some sort of rng state object that includes:

• real_type
• rng_state_type
• normal algorithm
• and the state

Then make overloads for things like

random_normal<real_type, algorithm, rng_state>(rng_state_type)

so that we can just write

random_normal(rng_state_type_wrapped)

something like

template <typename T>
typename T::real_type random_normal(T& state) {
  return random_normal<typename T::real_type, T::normal>(state.state);
}

See also #303 which is the same reallly