#21 Literal duplicate suppression

[Lars Heuer]

Better duplicate suppression: "+1"^^xsd:int is the SAME as "1"^^xsd:int.

Currently, we create two different literals for that

[Lars Heuer]

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Done for:
- xsd:boolean
- xsd:integer
- xsd:string
- xsd:decimal

[Lars Heuer]

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Partially supported:
- xsd:anyURI

Problem: http://example.org/ and hTtP://eXamPle.org are treated as a different IRIs

[Lars Heuer]

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2.0.0a2 contains better dupl.suppr. for:
- xsd:boolean
- xsd:integer
- xsd:string
- xsd:decimal