Phelel

- Numpy arraies of `dtype='long'` were changed to those of `dtype='int64'`.
- Collection of updates in velph commands.

- `--save` option was implemented for `velph-el_bands-plot` and
`velph-ph_bands-plot`. Without this option, the plot is shown on display.

- Collection of small updates of velph command

- Fix minor bugs in velph command

- Refactoring of `Phelel` class
- Major update of documentation

- Maintenance release to follow the change of phonopy.
- `elph_selfen_band_stop` is estimated from el-DOS instead of `elph_nbands` for
transport mode in velph.