Normalization part 2

Zhu's original comments:
> Normalization. This step scales the spectra so the average of the post edge region are moralized to one. This step mainly relies on “larch” package written by Eli.  The normalization in this step is different from the normalization in step 2, so we might need to change the name of one of them.

I think we can do this on our own without the `larch` package.