changed ACrossover interface to use VectorAdapter class to wrap STL vectors
removed obsolete header in PMXCrossover operator header
changed VectorAdapter interface: use reference instead of pointer
changed ACrossover interface: use reference instead of pointer
renamed xcrossover() to population_crossover()
added AIndexSelection::select_population() method
added missing using 'AGenome::instance' declaration to Genome class
renamed ACrossover::population_crossover() method to ACrossover::multi_crossover()
set base class access level in selection operators to 'public'
implementation of AMutation::multi_mutate() method