Serialization v. 2.0 (type safe + graceful error handling)

[bardram]

2.0.0

• type safe annotation in class factor method, like this; FromJsonFactory().fromJson<A>(json)
• graceful handling of errors when a non-known JSON type is encountered by allowing for a "notAvailable" parameter to the fromJson factory method, like this; FromJsonFactory().fromJson<B>(json, notAvailable: B(-1))
• refactor of universal unique IDs (UUIDs) to using the Uuid().v1 construct
• extending unit test coverage (incl., e.g. exceptions)
• improvement to examples in the example.dart file and documentation in the API doc and README

Fixes #414