HubMed UTF-8 export

Now that the NCBI have stopped messing around with character encodings, HubMed's RIS and BibTeX export should be working properly again. RIS export (eg for Endnote or Procite) replaces UTF-8 characters with their Latin-1 equivalents, while BibTeX export converts UTF-8 characters to their bracketed forms. Still no UTF-8 RIS export (which the newest version of Endnote can handle), but I have an idea for how to add that as an option.