Added
- Support for GlobRef definitions in a `pipeline.toml` file
  - Takes a `pattern` glob expression instead of an `input_path`
  - Takes a directory path as `output_dir` instead of a file path as `output_file`, and will construct the an `output_file` by appending the file name of a matched file to the output directory

Changed
- All paths in pipelines are now relative to the pipeline configuration file, instead of the current directory