function heading( text, level ) {
	var str = '\n\n';
	str += repeat( '#', level ) + ' ' + text;
	str += '\n\n';
	return str;
}
Returns a Markdown heading.

@private
@param {string} text - heading
@param {number} level - heading level
@returns {string} Markdown heading

@example
var out = heading( 'beep', 1 );
// returns '\n\n# beep\n\n'

@example
var out = heading( 'boop', 3 );
// returns '\n\n### boop\n\n'