0.5.8

• Much better diagnostics and error handling
• Instead of requiring the input to be realized immediately, it can be a
  Callable instead, that will be resolved if there is no doGenerate method
  that takes Callables. The result of the callable is used to resolve the
  actually invoked doGenerate method.
• Allow for absolute paths, by making sure not to resolve them against
  the base directory when they are absolute.