Spectrum doesn't support all slicing

[hughesadam87]

We are hard-coding index into Spectrum:

  out = cls(series.values, index=spectra.index)

However, what if I just sliced a single row and multiple columns. Then the index should be columns! I think this needs to be rectified somehow in the _transfer method() where this is called?

[hughesadam87]

Would probably have to figure out if these values are in the original spectra row-wise or column wise.

  out = cls(series.values, index=spectra.index)

vs

  out = cls(series.values, index=spectra.columns)