Equipment coverage stuff

This release adds support for reading the schema's equip region data, as well as getting item equip region information.

Added

• Native TF2Econ_GetItemEquipRegionMask, which returns an item's equip region mask that can be and'd together with another item's (or equip region's) mask to see if the items have overlapping equip regions.
• Native TF2Econ_GetItemEquipRegionGroupBits, which returns the item's equip region groups as a bitfield ([0, 28] left-shifted).
• Native TF2Econ_GetEquipRegionGroups, which returns a StringMap containing equip region names mapped to their group index. Equip regions under a shared subsection in the schema's equip_regions_list section have the same group index.
• Native TF2Econ_GetEquipRegionMask, which stores the group's mask given a valid group name.