Update E-Mail and Readme
Omit $0 from MARC 5XX description fields

In GBV data they may contain unsightly linking information à la:

<datafield tag="502" ind1=" " ind2=" ">
  <subfield code="0">(DE-601)105748641</subfield>
  <subfield code="0">(DE-588)118623222</subfield>
  <subfield code="a">Univ., Diss.--Gießen, 2008</subfield>
  <subfield code="a">Tolkien</subfield>
</datafield>
remove unused variable
update e-mail address