Added EZFormMultiRadioFormField form field capable of multiple selection.
Amended EZFormRadioChoiceViewController to allow multiple selection.
Updated EZForm registration form demo with an example of multiple selection fields.
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