Retain a stringbuilder to mutate the string rather than finalizing temporary strings
yields some speed improvements (less gen0 string objects allocated)
reduces loading time (don't have to allocate conversion arrays when
launching a gen7 game), and separates things to easier to manage
locations
reworks gen3 string encode/decode, no longer does 3->4->5 and 5->4->3;
instead goes straight to the end result without an intermediary format.
String sanitization should probably be broken up rather than reused, oh
well.
