Slightly improve docs for relation.hrefType.
Slightly improve docs for relation.hrefType.

slang800/assetgraph,papandreou/assetgraph,jscinoz/assetgraph,papandreou/assetgraph,slang800/assetgraph,jscinoz/assetgraph,assetgraph/assetgraph,papandreou/assetgraph,jscinoz/assetgraph