Use a single password_hash function

Using two different functions makes no sense in Python. A single
function with an optional argument is more Pythonistic.

libreauth/password.py

@@ -63,10 +63,7 @@ class LibreAuthPassError(Exception):
         else:
             self.message = 'unknown error'
 
-def password_hash(password):
-    return password_hash_standard(password, NOSTANDARD)
-
-def password_hash_standard(password, standard):
+def password_hash(password, standard=NOSTANDARD):
     pass_len = len(password)
     if pass_len < PASSWORD_MIN_LEN:
         raise LibreAuthPassError(1)