v1.3.0

V1.3.0 update:

• implemented download cache system
• make resolve_path more reliable.
• added get_details utility.
• source information is no longer loaded by default, as this is error prone and slow.
  To retrieve source information either explicitly pass the load_bib=TRUE flag to the
  cldf constructor or run o <- load_bib(o).
• removed citation() function as it namespace clashes with utils::citation,
  and is now added to the CLDF object as o$citation.
• added more documentation

Full Changelog: v1.2.0...v1.3.0