Played around with the constants to get the l=0 error to match the
sphere sets error.
Renamed the fisher-related files.
Remove the FFT/invFFT "fixers" (as they are not needed)
In the spherical harmonic variance derivation, fixed an unnecessary
integration over the solid angles, getting rid of (4pi)^2 factor.

Also made progress on the line-of-sight derivation.
Amended fisher_harmonics to reflect changes to the derivation.
Essentially, removed a factor of 4pi appearing in the spherical window.
Included a new function "trapznd" which will perform integration over
arbitrary dimensions.
Initial Commit, file to contain the line-of-sight calculations.