A new 'ParameterDict' has been added that automatically encodes and
decodes values when they are store in a dictionary. The dictionary uses 2 characters
prefixed to each value to store the original type information, e.g. 'fl' -> list of
floats, before being passed through a url encoder. The reverse process happens on retrieval.
To access the encoded values an `iterEncodedItems` and `getEncodedValue` methods have been added.
The appropriate unit tests have also been added.
list_or_* functions (e.g. list_or_string) will now always return a list,
however will accept lists or indivitual values. Also added a list_or()
generator function, similar to what already exists for list_of().
