BetterCaptcha | 使用位图创建验证码的图片，非常可配置。
示例代码：
using System.Collections.Generic;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Drawing.Text;
using System.Linq;
using System.Threading.Tasks;
string captchaCode = Program.captchaCode(5);
var captcha = Program.generateCaptchaImage(400, 200, HatchStyle.Percent90, captchaCode, new FontFamily("Hometown"), Fo
