Added a check if specified path exists.
Added a check if specified path open error.
Aboid the error when specified the following path.

- On Windows
- Path is surronded by double quotation
- Last string of path is path separator
[WIP] add Modifier interface
[WIP] use bytes.Buffer
[WIP] slightly changes
[WIP] slightly changes
[WIP] optimized (remove bytes.Buffer)