BibFormat: new configuration of full-text snippets
BibFormat: new configuration of full-text snippets

* New configuration of full-text snippet facility with limits
  based on characters rather than words.  Changes configuration
  syntax to allow for multiple snippet settings for multiple
  document types.  The limits on the number of snippets to show
  and on the number of characters to show in each snippet can now
  be set differently for every different document status type.
  Useful in case of different agreements with different publishers.
  (closes #45)

Co-authored-by: Tibor Simko <c7116e45300b163846dc01f3ed02116e3f8ef7a5@cern.ch>

inveniosoftware/invenio-formatter,tiborsimko/invenio-formatter,tiborsimko/invenio-formatter,inveniosoftware/invenio-formatter,inveniosoftware/invenio-formatter,tiborsimko/invenio-formatter