Biblio:  Put bibliography in 'references' metadata field.

(Instead of just tacking it on to the end of the document.)

This will require changes in default templates (addition of
'references' field) and possibly a special-case for 'references' in
the writers that write all metadata fields (assuming we don't want the
entire bibliography repeated at the beginning of a document in e.g. reST).
Templates:  Added 'references' variable for bibliography.

Previously the bibliography was just tacked on to 'body'.  Now
it is a separate variable, so you can put it where you like,
style it as you like, etc.
Test suite:  Use `-s` for markdown citation tests.

This is needed because the 'references' variable is now used
for the bibliography.
Markdown & RST writers: Omit 'references' from metadata block at top.

Otherwise we get references repeated in two places.
Merge branch 'issue771' into altcite

Conflicts:
	data/templates
	src/Text/Pandoc/Writers/Markdown.hs
	tests/Tests/Old.hs