Update 'items' and 'inventory' modules / interfaces to work with Spigot

[walterhiggins]

SpigotMC uses Bukkit's Material Enum in place of CanaryMod's ItemType Enum.

Need to update generateItemTypes.js and inventory module accordingly
(Ideally to work with both CanaryMod and Spigot - though enums will be different)

[walterhiggins]

Update: The items and inventory modules are already cross-platform (work with both SpigotMC and CanaryMod) - only the API documentation needs to be updated (for SpigotMC)