OBX pdf pointers

[Anthony Master]

I have worked with a few interfaces now that embed or reference PDF files into OBX segments. Until #15 is fully supported (and maybe even after), there is a need to be able to pick these files up from one references location, place them in another location, and update the reference in the OBX outbound.

Also may be useful for converting between embedded/referenced PDF documents. For example, the source embeds the document, and the destination wants the file on a sftp server and referenced in the HL7. May depend upon #8