Created method to supply an estimated size per Apache prefork child

This method "go_estimate_RAM_per_prefork_child" uses code from https://github.com/gusmaskowitz/apachetuner to calculate the average size of each prefork child in Apache. 

I only run the check if the prefork MPM is found. The resulting value is not a string so ready for more calculations 

I.E using it to multiply with the MaxClients value to see how much RAM we promise Apache in order to make a recommendation.