refactored StringSmoothTest
removed MutableFile, MutableFileSet, MutableStoredFile, MutableStoredFileSet
removed StoredFileSet, StoredFile
renamed FakeFileSystem.createFileWithContent() -> createFile()
removed FakeFileSystem.createEmptyFile() and replace usages with .createFileContainingItsContent()
refactored NewFileFunction
changed charsets used by NewFileFunction
fixed style in OutputClassFile