Add coding exercises for Facebook interviews

Add attempts at solving coding problems to Briefcase.

scratch/facebook/reverse-string-in-place.py

@@ -0,0 +1,14 @@
+# reverse :: [Char] -> ()
+def reverse(xs):
+    i = 0
+    j = len(xs) - 1
+    while i < j:
+        xs[i], xs[j] = xs[j], xs[i]
+        i += 1
+        j -= 1
+
+xs = [list("testing"), list("a"), list("to")]
+for x in xs:
+    print(x)
+    reverse(x)
+    print(x)