assets: add back Boost assets

sonic-boost.love/assets/fonts/CREDITS.txt

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+## Imperium Porcorum - Fonts Credits
+
+- [Teko Bold](https://github.com/itfoundry/teko) by the [Indian Type Foundry](https://github.com/itfoundry) - Open Font License 
+
+- [Russian One](https://fonts.google.com/specimen/Russo+One) by Jovanny Lemonad - Open Font License
+
+- [Pixel Operator](https://notabug.org/HarvettFox96/ttf-pixeloperator) by [Harvett Fox 96](https://notabug.org/HarvettFox96) - Creative Commons 0

sonic-boost.love/assets/sprites/items/crystal.lua

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+return {
+  metadata = {
+    height      = 16,
+    width       = 16,
+    defaultAnim = "default"
+  },
+  animations = {
+    ["default"] = {
+      startAt     = 1,
+      endAt       = 1,
+      loop        = 1,
+      speed       = 0,
+      pauseAtEnd  = true,
+    },
+  }
+}

sonic-boost.love/assets/sprites/items/ring.lua

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+return {
+  metadata = {
+    height      = 16,
+    width       = 16,
+    defaultAnim = "default"
+  },
+  animations = {
+    ["default"] = {
+      startAt     = 1,
+      endAt       = 8,
+      loop        = 1,
+      speed       = 8,
+      pauseAtEnd  = false,
+    },
+  }
+}