options:
[-in <filename>] converts file <filename> to inches
[-mm <filename>] converts file <filename> to millimeters
[-d] sets the current directory as the source
[-d <dirname>] sets directory <dirname> as the source 设置一个目录内的文件要求转换
[-o <dirname>] sets existing directory <dirname> as the destination 设置转出目录
[-s] traverses subdirectories
[-u] converts udf files
[-uo] converts udf files only
[-x] exports the expressions of the converted part
[-y] converts entire assembly