Don't eat the namespace, and use pcall

Also move OnLogin to event handler metatable

modules/event.lua

@@ -337,6 +337,24 @@ addon = setmetatable(addon, {
 					return true -- unregister event
 				end
 			end)
+		elseif key == 'OnLogin' then
+			--[[ namespace:OnLogin()
+			Shorthand for the [`PLAYER_LOGIN`](https://warcraft.wiki.gg/wiki/PLAYER_LOGIN).
+
+			Usage:
+			```lua
+			function namespace:OnLogin()
+			    -- player has logged in!
+			end
+			```
+			--]]
+			addon:RegisterEvent('PLAYER_LOGIN', function(self)
+				local successful, ret = pcall(value, self)
+				if not successful then
+					error(ret)
+				end
+				return true -- unregister event
+			end)
 		elseif IsEventValid(key) then
 			--[[ namespace:_event_
 			Registers a  to an anonymous function.

modules/load.lua

@@ -15,28 +15,13 @@ function addon:HookAddOn(addonName, callback)
 	end
 end
 
-function addon:ADDON_LOADED(addonName)
+addon:RegisterEvent('ADDON_LOADED', function(self, addonName)
 	for _, info in next, addonCallbacks do
 		if info.addonName == addonName then
-			info.callback()
+			local successful, err = pcall(info.callback)
+			if not successful then
+				error(err)
+			end
 		end
 	end
-end
-
-function addon:PLAYER_LOGIN()
-	--[[ namespace:OnLogin()
-	Shorthand for the [`PLAYER_LOGIN`](https://warcraft.wiki.gg/wiki/PLAYER_LOGIN).
-
-	Usage:
-	```lua
-	function namespace:OnLogin()
-	    -- player has logged in!
-	end
-	```
-	--]]
-	if addon.OnLogin then
-		addon:OnLogin()
-	end
-
-	return true
-end
+end)