Add new enemy, refactor a bit, add armor.

src/enemy/ebi.lua

@@ -0,0 +1,14 @@
+-- A shrimp-like enemy unit
+import "CoreLibs/object"
+import "CoreLibs/graphics"
+import "CoreLibs/sprites"
+import "entity"
+
+local gfx <const> = playdate.graphics
+
+class("Ebi").extends(Entity)
+
+function Ebi:init()
+   local img = gfx.image.new(10, 10, gfx.kColorBlack)
+   Ebi.super.init(self, img, 5)
+end

src/enemy/ika.lua

@@ -0,0 +1,14 @@
+-- A squid-like enemy unit
+import "CoreLibs/object"
+import "CoreLibs/graphics"
+import "CoreLibs/sprites"
+import "entity"
+
+local gfx <const> = playdate.graphics
+
+class("Ika").extends(Entity)
+
+function Ika:init()
+   local img = gfx.image.new(50, 50, gfx.kColorBlack)
+   Ika.super.init(self, img, 25, 1)
+end