EvolutionSet was just an object that hides an array, with no logic
was planning to use the EvolutionSet to do the evolution checks, but
EvolutionTree was required to connect the evolution chains together
reduce nesting (evo.RequiresLevelUp is checked twice, only check once
and handle path)
compact some methods
seal some classes
add a little xmldoc to exposed members
Too many classes in the same file, break up.
simplify things a little in EncounterArea (remove passing thru nulls,
should throw excpetion immediately if misconfigured).
