Adding additional documentation to MultiRadioFormField
Altered behaviour of unsetActualFieldValue: to behave the same was as setActualFieldValue: the delegate will be called regardless of whether the field value was changed by the attempt to unset the value see [EZFormField.m]

[1]: https://github.com/chrismiles/EZForm/blob/1.1.0/EZForm/EZForm/src/EZFormField.m#L54
Added a mutually exclusive option to the multi radio field
Updated the demo project to demonstrate the mutually exclusive option