[ACTION-254] Edit usages URI to IRI

Hi,

I hope that I have successfully completed this action. Intentionally I
haven't blindly changed all URI -> IRI

- I left namespace URIs in place
- I haven't touched terminology mentioned in NIF conversion algorithm
- I haven't changed "Provenance URI" because I wasn't sure if IRI is
appropriate here

     Jirka

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  Jirka Kosek      e-mail: jirka@kosek.cz      http://xmlguru.cz
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