Added age-combining-function for multi-parent genetic operators, default = max.
Added age-combining-function for multi-parent genetic operators, default = max.

NicMcPhee/Clojush,lspector/Clojush,Vaguery/Clojush,saulshanabrook/Clojush,NicMcPhee/Clojush,thelmuth/Clojush,lspector/Clojush,Vaguery/Clojush,saulshanabrook/Clojush,thelmuth/Clojush