Refactor file metadata #45
Description
With repeat now being a thing, there is no longer a one input file > one output file match. This is not really reflected in the types though. I think FileMetadata needs to be split into SourceFileMetadata and OutputFileMetadata or something. We need OutputFileMetadata for rendering output files, and SourceFileMetadata for get_file / get_files (maybe there should be a way of getting all output files for one source file?).