Add spectral decomposition to lalsimulation and fix rho calculation

@jolien-creighton : I've added the spectral decomposition as a new file. I think I've linked things properly, but you might want to check. I tried copying the format of code already there. I've built and run a few tests, which worked. Ex:

$ lalsim-ns-mass-radius -S -w 1.0 -x -1.0 -y 0.3 -z 0.1
$ lalsim-ns-params -S -w 1.0 -x -1.0 -y 0.3 -z 0.1
$ lalsim-ns-eos-table -S -w 1.0 -x -1.0 -y 0.3 -z 0.1

Additionally, this has a fix to calculate rho for the tabular code.

Please let me know if there's anything you'd like to see changed.