Spearhead API updates (#31)

Co-authored-by: dutchie032 <dutchie032>

classes/api/SpearheadApiDoc.lua

@@ -0,0 +1,17 @@
+---@class SpearheadAPI
+---@field Stages SpearheadStagesAPI
+---@field Missions MissionAPI
+SpearheadAPI = SpearheadAPI
+
+---@class SpearheadStagesAPI
+---@field changeStage fun(stageNumber: number): boolean, string @Changes the active stage of spearhead. <br/> All other stages will change based on the normal logic. (CAP, BLUE etc.)
+---@field getCurrentStage fun(): number | nil @Returns the current stange number <br/> Returns nil when the stagenumber was not set before ever, which means Spearhead was not started.
+---@field isStageComplete fun(stageNumber: number): boolean | nil, string @returns whether a stage (by index) is complete. <br/> @param stageNumber number <br/> @return boolean | nil <br/> @return string
+
+---@class OnMissionCompleteListener
+---@field onMissionComplete fun(self: OnMissionCompleteListener, zone_name: string) @Called when a mission is completed. @return void
+
+---@class MissionAPI 
+---@field addOnMissionCompleteListener fun(listener: OnMissionCompleteListener) @Adds a listener to the mission. <br/> @param listener OnMissionCompleteListener <br/> @return void
+
+