Note: addition of relation definition rules to the ABNF

In reviewing the Dictionary section of the XDI Core draft, I realized that we had not included rules for dictionary statements defining relations. Unlike contextual and literal definitions, relation definitions use special predicates as defined in the Relations section of the XDI Dictionary Patterns page on the wiki. 

So I added these rules (12 in total) to the ABNF. See the change log at:

https://wiki.oasis-open.org/xdi/XdiAbnf

=Drummond