Setting the value of a read-only field should update the label. Fixes #5
Should be able to make mult-select lookup fields read-only (fixes #6).
Refactored read-only methods to be class-level methods.
Added some tests for MakeReadOnly.
Deprecate Debug mode (throw exceptions instead).
Added HideSPField, ShowSPField, and GetSPFields public methods back.
Refactored how global SPUtility variable is set(again).