[simplify interface] Clarify use of expand_parameters, strategy_list, hyperpar

[dfalster]

The functionality and role of different parts is a little murky for users.

To consider

• rename expand_parameters so purpose is more explicit? add_strategies?
• rename strategy_list really in turns a trait_matrix into a strategy object. Perhaps generate_startegy and take this to highest level, i.e. not run as embedded function?
• Make need and role of hyperpar more apparent?