Minor edits to the variableRepresentation section

- Removed second example as they only differed in the property used
- Add variableRepresentation to the example
- Converted the description of BasicRepresentation and ExplicitRepresentation from a definition list to a simple paragraph to be consistent with the rest of the document
- Moved warning up
- Added an exemplary IRI Template to the example comparing the two representation formats

This addresses #30.