Add ground rule tile + tile palette + example scene (#64)

* Install 2D Tilemap + 2D Tilemap Extras

* Install ProBuilder

* Add ProBuilder settings

* Add ground tile prefabs

* First stab at tiles

* Fix up some more cells

* Finish up tileset

* Update

* Clean up sandbox scene

* Reset game scene

* Clean up project dir

* Re-disable water visual

* Revert

* Update

* Update workflow document

* Update palette prefab

* Update stylized water 2 test scene

* Some minor updates to get rid of sprites on rule tile

* Update readme

.github/PULL_REQUEST_TEMPLATE/create_a_3d_tileset.md

@@ -0,0 +1,12 @@
+## Workflow
+
+1. Create a Rule Tile (Project → Create → 2D → Tiles → Rule Tile).
+2. Create a Tile Palette (Window → 2D → Tile Palette).
+3. Drag new Rule Tile onto palette.
+4. On the new Tilemap (created by step 2 above), change the swizzle to XZY.
+5. Select your rule tile in your palette, and paint on the new Tilemap.
+6. Use the new Tilemap to define tile rules in your Rule Tile.
+    1. Remember: red arrow means no hit, green arrow means hit.
+    2. Add a default sprite to make the rule tile visible in your Tile Palette.
+7. Once you feel you’ve covered enough edge cases, you’re done!
+    1. There might be more edge cases, but it’s best to discover them when integrating your game end-to-end, so as to avoid unneeded work.

Assets/Audiovisuals/Materials/polyperfect/atlas-night-LPUP.mat

@@ -11,7 +11,6 @@ Material:
   m_Shader: {fileID: 4800000, guid: 933532a4fcc9baf4fa0491de14d08ed7, type: 3}
   m_ValidKeywords:
   - _EMISSION
-  - _METALLICSPECGLOSSMAP
   - _SPECGLOSSMAP
   - _SPECULAR_SETUP
   m_InvalidKeywords: []