List the files stored for a PCB version.

Each file has a state:

• original - a file as you uploaded it (for example an EDA board file or a design archive).
• processed - a file recognized from your upload and assigned to a layer.
• generated - a file MacroFab generated from your design (for example gerbers exported from
  an EDA board file, or preview images).
• extra - supplemental files attached to the PCB.
• pending - uploaded files that have not yet been accepted into the PCB.
• trash - files that have been deleted.

Download a file with GET /api/v3/pcb/{pcb_id}/{pcb_version}/file/{state}/{file_name}, using
its state and basename.