function cloneLine(line) {
	var result = new Line(line.maxWidth);

	for (var key in line) {
		if (line.hasOwnProperty(key)) {
			result[key] = line[key];
		}
	}

	return result;
}
Executes layout engine on document-definition-object and creates an array of pages
containing positioned Blocks, Lines and inlines

@param {Object} docStructure document-definition-object
@param {Object} fontProvider font provider
@param {Object} styleDictionary dictionary with style definitions
@param {Object} defaultStyle default style definition
@return {Array} an array of pages