BibFormat: additions to the HepNames HD display

 * BFE providing link to arXiv using arXiv author IDs found in MARC
 * modified Hepnames_HTML_detailed.bft to include arXiv BAI link
 * some unit tests for this format element

Signed-off-by: Thorsten Schwander <thorsten.schwander@gmail.com>
Merge pull request #52 from tsgit/hepnames_arxiv2

BibFormat: additions to the HepNames HD display