winfrom对话框选择文件时候的过滤设置

对话框选中文件时候的过滤设置，记录下

public const string ImageFilter = "Image files (*.jpg, *.jpeg, *.jpe, *.jfif, *.png,*.gif,*.bmp) | *.jpg; *.jpeg; *.jpe; *.jfif; *.png;*.gif;*bmp"; 
public const string PDFFilter = "PDF files (*.pdf) | *.pdf"; 
public const string ExcelFilter = "Excel Files|*.xls;*.xlsx;*.xlsm";