Cannot construct pre-computed matrices for Yb3+

[mccoylim]

When calling dieke.RareEarthIon(nf) for nf=13 (which corresponds to the number of f-electrons Yb3+ has), the readcrosswhite() function in this class tries to call the file "data/f1nm.dat", which does not exist in the package.

[jevonlongdell]

The reason for this is that for Yb there is only one hole in the 4f states. This means that the L and S matricies don't need etc to be read from the crosswhite files they can be 'easily' be calculated. I'm not sure when I'll get around to doing it.