velph phelel vs supercell naming conflict

[mystery-e204]

When running velph phelel init, a directory named phelel is created. However, when creating a self-energy calculation from this supercell data via velph elph generate, it assumes that the directory is called supercell (which was the case in the past). I think this should be consistently called phelel as well.

[atztogo]

Thanks for your report. I think it is fixed by PR #29. I should write a test. But I don't have a good idea how to write the test for those commands systematically. Probably in the future I will work on it.

Note, in addition, I changed the command name from velph-elph to velph-transport. See #29.