Add example of 'woods' operational semantics. Clearer error messages. Implement full OD-API. Small refactoring of Conformance class.

util/prompt.py

@@ -14,4 +14,26 @@ def yes_no(msg: str):
 
 def pause():
    print("press any key...")
-   input()
+   input()
+
+def choose(msg:str, options):
+   arr = []
+   for i, (key, result) in enumerate(options):
+      print(f"  {i}. {key}")
+      arr.append(result)
+   if len(arr) == 0:
+      return
+   return __choose(msg, arr)
+
+def __choose(msg: str, arr):
+   sys.stdout.write(f"{msg} ")
+   try:
+      raw = input()
+      choice = int(raw) # may raise ValueError
+      if choice >= 0 and choice < len(arr):
+         return arr[choice]
+   except ValueError:
+      pass
+
+   print("Invalid option")
+   return __choose(msg, arr)