init rust db backend

lootalot_db/migrations/2019-06-10-124013_create_looted/down.sql

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+DROP TABLE looted;

lootalot_db/migrations/2019-06-10-124013_create_looted/up.sql

@@ -0,0 +1,8 @@
+CREATE TABLE looted (
+  id INTEGER PRIMARY KEY,
+  player_id INTEGER NOT NULL,
+  item_id INTEGER NOT NULL,
+  acquired_date DATE DEFAULT NOW,
+  FOREIGN KEY (player_id) REFERENCES players(id),
+  FOREIGN KEY (item_id) REFERENCES items(id)
+);