Not all arrays were being fully flattened

If a variable has the format y=[[2.]] for each update, then the saver contains
[[[2.]], [[3.]], ...] and after flattening it was a 2D colmn array. This
is a bug, and I changed it to flatten that 2D column array to a 1D
array.

Author: rlabbe

filterpy/common/helpers.py

@@ -205,6 +205,10 @@ def flatten(self):
                 shape = arr.shape
                 if shape[2] == 1:
                     self.__dict__[key] = arr.reshape(shape[0], shape[1])
+                arr = self.__dict__[key]
+                shape = arr.shape
+                if len(shape) == 2 and shape[1] == 1:
+                    self.__dict__[key] = arr.ravel()
             except:
                 # not an ndarray or not a column vector
                 pass