v0.6.1+1
- Added spanForElement; returns aSourceSpanfor an analyzerElement.
- Logs a warning to the console when a GeneratorBuilderoutputs a part file
 for a given input, but that input does not definepart 'name.g.dart';.
spanForElement; returns a SourceSpan for an analyzer Element.GeneratorBuilder outputs a part filepart 'name.g.dart';.