function plugin( dir, cwd, subpath ) {
	var opts;
	var args;
	var proc;

	opts = {};
	opts.cwd = dir;

	args = [];

	// Environment variables:
	if ( subpath ) {
		args.push( 'MARKDOWN_ASSET_PATH='+subpath );
	}
	// Target:
	args.push( 'markdown-asset-link' );

	proc = spawn( 'make', args, opts );
	proc.on( 'error', onError );
	proc.stdout.on( 'data', stdout );
	proc.stderr.on( 'data', stderr );
	proc.on( 'close', onFinish );
}
Plugin to generate an asset link for inclusion in Markdown files.

@param {string} dir - Makefile directory
@param {string} cwd - current working directory
@param {string} subpath - subdirectory path