Eval: During compiling call an eval function
Eval: try to guess possible values for given input parameters
Eval::possible_values(): resolve sets in possible return values
Eval::possible_values(): always return set of values
Stat::property_values(): try to resolve eval functions

- by using eval.possible_values()
Parser::parse_value(): accept calculations without eval()

- remove legacy rgb() parser
Eval: set mutability for many functions

- TODO: need to fix mutability for values with unit
Eval: config mutable may be a function
Eval: mutability dependend on parameters