New bibtex/biblatex handling, not via bibutils.

Moved bibtex2pandoc code to Text.CSL.Input.Bibtex.  We now use
biblio2yaml to do what bibtex2pandoc used to do.

Moved blocksToString and inlinesToString from Text.CSL.Pandoc
to Text.CSL.Input.Pandoc.
Removed bibtex2pandoc.