Add coding exercises for Facebook interviews

Add attempts at solving coding problems to Briefcase.

scratch/facebook/stock-price.py

@@ -0,0 +1,16 @@
+def max_profit(xs):
+    buy = xs[0]
+    profit = xs[1] - xs[0]
+    for price in xs[1:]:
+        profit = max(profit, price - buy)
+        buy = min(buy, price)
+    return profit
+
+xs = [([10,7,5,8,11,9], 6),
+      ([10,8,7,6,5], -1)]
+
+for x, expected in xs:
+    result = max_profit(x)
+    print(x, result)
+    assert result == expected
+    print("Success!")