Added typedefs: mapsec_t, metloc_t, and variants for MAPSEC and METLOC values. There are some rough edges that could do with smoothing out, but for now, this gets us close to ideal with a ROM that compares equal.
Per feedback, all typedefs to mention the underlying type within the typedef name. The documentation comments reflect and explain the naming convention.
Updated comments to reflect the fact that we're no longer using SET8 for a Pokemon's met locations, in favor of a new macro (added by this PR) that adjusts to match the width of whatever is being set.
