Add PICA-XML-Exchange format used in Folio?

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The CBS2Folio conversion uses a non-standard XML format for wrapping PICA records. In particular the XML has

• no XML namespace
• addditional fields status, hrid (these are the only parts not fully convertible to/from other PICA serializations)
• datafields wrapped in new element metadata
• datafields of item records grouped by epn in new element item
• additional attribute fulltag (seems to be derived from tag and occurrence, so can be generated automatically)

If this format is rather a fluid ad-hoc tool, it may make more sense to put conversion from and to this format into the cbs2folio-transformations repository. Otherwise support in PICA::Data makes sense because it facilitates direct conversion between all other PICA serialization forms, syntax highlighting and querying.

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See als conversion script from PICA to import format. There is some special treatment of x-occurrences as well.

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Implemented but writer missing test.