Improved and more consistent naming of objects.

This release contains a few (minor) breaking changes. Generated 2.x ID's are still compatible with 3.x ID's.

• Most of the constructor overloads for the IdGenerator have been replaced with a single constructor which accepts IdGeneratorOptions that contains the ITimeSource, IdStructure and SequenceOverflowStrategy.
• The MaskConfig class is now more appropriately named IdStructure since it describes the structure of the generated ID's.
• The UseSpinWait property has moved to the IdGeneratorOptions and is now an enum of type SequenceOverflowStrategy instead of a boolean value. Note that this property has also been renamed in the config file (from useSpinWait to sequenceOverflowStrategy) and is no longer a boolean but requires one of the values from SequenceOverflowStrategy.
• ID is now Id (only used as return value by the FromId(...) method)