Add coding exercises for Facebook interviews

Add attempts at solving coding problems to Briefcase.

scratch/facebook/node.py

@@ -0,0 +1,38 @@
+class Node(object):
+    def __init__(self, value, left=None, right=None):
+        self.value = value
+        self.left = left
+        self.right = right
+
+    def insert_left(self, value):
+        self.left = Node(value)
+        return self.left
+
+    def insert_right(self, value):
+        self.right = Node(value)
+        return self.right
+
+tree = Node(
+    50,
+    Node(
+        17,
+        Node(
+            12,
+            Node(9),
+            Node(14),
+        ),
+        Node(
+            23,
+            Node(19),
+        ),
+    ),
+    Node(
+        72,
+        Node(
+            54,
+            None,
+            Node(67)
+        ),
+        Node(76),
+    ),
+)