Moved ExampleFragments dependency to specification
Renamed `ThrowableFailure` to `Failure` and added `withMessage` to
`ThrowingAssertions`
Moved code extraction of `ExampleFragments` to `io.Source`
Moved `FragmentBodyEnhancement` to it's own file
Moved around a lot of classes. Also moved some of the tests to the
documentation package, they include examples.