fixed a few first run errors with caching version (syntax errors etc)
preserve same URIs as original umls2rdf, and don't use bare prefixes, so all files produced use exactly the same set of prefixes
merging
add time to logs, and write out the write prefixes (wrong due to a merging error)
deleted obsolete files and updated README
by default, add in an explicit link usin rdfs:isDefinedBy to the source ontology
RDF we were generating was invalid. We can't use prefixes when the part after the prefix has any non-alphanumeric chars in it. However, we can use the @base specifier, so we can still have nice compact .TTL files