Handle MultiMarkdown-style citations.
This is a borrowed idea (1, p. 23).
This is a cited blockquote without a page reference. (2).
And a plain paragraph.
And a code block that is not a citation:
This is not a citation[p. 5][#Doe:1996].
And a work by Johnson that is not cited, but should be included in bibliography:
And multiple citations. (1, p. 3) (2, p. 10)
How about a citation within a footnote? 1
 John Doe. Some Book. Blog Books, 1996.
 James Smith. Some interesting paper. Some Journal, 1(2): 101-123, 2005.
 Bill Johnson. Some Book. Blog Books, 1996.