function cmd( src, dest, opts ) {
	var out = [];
	out.push( 'pandoc' );
	out.push( '--filter=pandoc-citeproc' );
	out.push( '--from=markdown' );
	out.push( '--to=markdown_github' );
	out.push( '--bibliography='+opts.database );
	out.push( '--csl='+opts.csl );
	out.push( '--output=' + dest );
	out.push( src );
	return out.join( ' ' );
}
Returns a command to convert a Markdown file containing citations to a Markdown file with a formatted bibliography.

@param {string} src - source file
@param {string} dest - destination file
@param {Options} opts - function options
@param {string} opts.database - path to a bibliography database file
@param {string} opts.csl - path to a Citation Style Language (CSL) file
@returns {string} command