Add relative number support for .ol files
Usually, one would say maximum age for an EA is half of the max-generation number, or 40% of the population should be chosen by an elite selector. For one setting, absolute numbers suffice. However, when constructing several files and varying parameters, this is a source for mistakes, because every change has follow-up-changes. Would be great to have something like maximum-age:= 0.5 of 'number-of-generations'. Sth like that.