Update edges

[mretegan]

Added a few missing ones and a short definition.

[maurov]

@mretegan thanks for your work on this.

For the edges, I think we should allow only the IUPAC notation. Contrary to the emission lines, it is rather simple to identify the edge in IUPAC notation. The ASCII notation is misleading because it can be either written in LaTeX or another way. I would keep the ASCII notation in the documentation, but the enumeration should keep only IUPAC.

Again, I find clear how is stated in the XrayDB documentation: https://xraypy.github.io/XrayDB/overview.html#x-ray-edges

[mretegan]

@maurov Okay, I updated the definition.

[maurov]

OK to merge!