[Keyboard] Concertina (#11922)

* [Keyboard] Concertina

* Added a novel handwired keyboard.

* Concertina lint

* Perfunctory changes to pass CI.

* Concertina line width

* Changes from code review: GPL headers, modernization, full-width
  representation of matrix to match info.json.

keyboards/handwired/concertina/info.json

@@ -0,0 +1,37 @@
+{
+    "keyboard_name": "Concertina",
+    "url": "https://viktor.eikman.se/article/the-concertina/",
+    "maintainer": "veikman",
+    "width": 12,
+    "height": 8,
+    "layouts": {
+        "LAYOUT_64key": {
+            "key_count": 64,
+            "layout": [
+                {"x":2, "y":0.5}, {"x":3, "y":0}, {"x":4, "y":0.3},
+                {"x":8, "y":0.7}, {"x":9, "y":0.3}, {"x":10, "y":0},
+
+                {"x":2, "y":1.5}, {"x":3, "y":1}, {"x":4, "y":1.3}, {"x":5, "y":0.7},
+                {"x":8, "y":0.7}, {"x":9, "y":1.3}, {"x":10, "y":1}, {"x":11, "y":1.5},
+
+                {"x":3, "y":2}, {"x":4, "y":2.3}, {"x":5, "y":1.7},
+                {"x":8, "y":1.7}, {"x":9, "y":2.3}, {"x":10, "y":2},
+
+                {"x":2, "y":4}, {"x":3, "y":4}, {"x":4, "y":4}, {"x":5, "y":4},
+                {"x":8, "y":4}, {"x":9, "y":4}, {"x":10, "y":4}, {"x":11, "y":4},
+
+                {"x":0, "y":5}, {"x":1, "y":5}, {"x":2, "y":5}, {"x":3, "y":5}, {"x":4, "y":5}, {"x":5, "y":5},
+                {"x":8, "y":5}, {"x":9, "y":5}, {"x":10, "y":5}, {"x":11, "y":5}, {"x":12, "y":5}, {"x":13, "y":5},
+
+                {"x":0, "y":6}, {"x":1, "y":6}, {"x":2, "y":6}, {"x":3, "y":6}, {"x":4, "y":6}, {"x":5, "y":6},
+                {"x":8, "y":6}, {"x":9, "y":6}, {"x":10, "y":6}, {"x":11, "y":6}, {"x":12, "y":6}, {"x":13, "y":6},
+
+                {"x":0, "y":7}, {"x":1, "y":7}, {"x":2, "y":7}, {"x":3, "y":7}, {"x":4, "y":7},
+                {"x":9, "y":7}, {"x":10, "y":7}, {"x":11, "y":7}, {"x":12, "y":7}, {"x":13, "y":7},
+
+                {"x":3, "y":8},
+                {"x":10, "y":8}
+            ]
+        }
+    }
+}