输入验证类

　　This is a simple class implements several rules to validate text values on the server side, eventually submitted by the user in Web forms.
　　Currently it implements the following validation rules:
　　- E-mail address
　　- Signed integer number
　　- Unsigned integer number
　　- Alphanumeric text with letters, digits and spaces
　　- Date formatted as MM/DD/YYYY or MM-DD-YYYY