Encapsulates metadata for the input stream to a {@link ResourceMigrator}.
The input stream for resource migration can vary in its origin (eg. file, socket), which can influence the processing of migration steps. For example, a file-based input stream may use a {@link PathRecogniser} to help identify the type ofmigration to perform, whereas a socket-based input stream may rely on a {@link ContentRecogniser} only.
@see ResourceMigrator#migrate(String,java.io.InputStream,OutputCreator)
@mock.generate
@todo replace with an InputSource style object which contains data and metadata
@todo use the Content* interfaces for flexibility.