reducing allocations, increasing clarity by removing some magic numbers
probably can rewrite some of the evo loading/checking for even less, but
good for now.
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).
