实现标题不缩进，所有内容缩进

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 NSMutableParagraphStyle *style = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
 // 对齐方式
 style.alignment = NSTextAlignmentJustified;
 // 首行缩进
 style.firstLineHeadIndent = 0.0f;
 style.paragraphSpacing = 2;
 // 头部缩进
 style.headIndent = 40.0f;
 // 尾部缩进
 style.tailIndent = -40.0f;
 NSString *title = @"第一.";
 NSMutableAttributedString *attrText = [[NSMutableAttributedString alloc] initWithString:title attributes:@{ NSParagraphStyleAttributeName : style}];
 UILabel *tool = [UILabel new];
 tool.attributedText = attrText;
 [tool sizeToFit];
 CGFloat head = CGRectGetMaxX(tool.frame) + 0;
 NSLog(@"%f",head); // 49.666667 39.666667
 title = @"利用 NSMutableParagraphStyle 实现文字缩进,利用 NSMutableParagraphStyle 实现文字缩进,利用 NSMutableParagraphStyle 实现文字缩进,利用 NSMutableParagraphStyle 实现文字缩进,利用 NSMutableParagraphStyle 实现文字缩进,利用 NSMutableParagraphStyle 实现文字缩进"
 @"利用 NSMutableParagraphStyle 实现文字缩进";
 style = [[NSParagraphStyle defaultParagraphStyle] mutableCopy];
 // 对齐方式
 style.alignment = NSTextAlignmentJustified;
 // 首行缩进
 style.firstLineHeadIndent = head;
 // 头部缩进
 style.headIndent = head;
 NSAttributedString *contentAttrText = [[NSAttributedString alloc] initWithString:title attributes:@{ NSParagraphStyleAttributeName : style}];
 [attrText appendAttributedString:contentAttrText];
 UILabel *label = [[UILabel alloc] initWithFrame:frame];
 label.numberOfLines = 0;
 label.attributedText = attrText;
 label.backgroundColor = [UIColor yellowColor];
 [self.view addSubview:label];