feature: compute the 2-point correlation function in easyeq.
feature: compute the Fourier transform of the 2-point correlation function
in anyeq and easyeq.
feature: compute the local maximum of the 2-point correlation function and
its Fourier transform.
feature: compute the compressibility for anyeq.
feature: allow for linear spacing of rho's.
feature: print the scattering length.
change: ux and uk now return real numbers.
fix: error in the computation of the momentum distribution: wrong
definition of delta functions.
fix: various minor bugs.
optimization: assign explicit types to variables.
