Eval: move base functions to pgmapcss.eval.base.py
Eval: start to move config to files; read config by executing code
Eval: Move config of other function to config classes
Eval: remove eval_
Eval: check validity of function names
Eval: move function compiling to config classes
Eval: better integrate config classes
Eval: fix eval tests
Eval: rewrote eval tests
Colors::color_values: bugfix
Eval::cond: add eval tests
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