* Fixed a normalisation bug in the hybrid Poisson solver
* Added calculation of the exact T(r=0) by summing modes rather than by analytical integration
* Fixed a bug in the deconvolution that caused the Nyquist mode to be excluded in the deconv.
* Fixed a bug in the random number generator when using single thereaded FFTW.
New conservative transfer function scheme.
New random number generator that preserves coarse Fourier modes instead of applying Hoffman-Ribak
Some minor bugs fixed.
* Moved hybrid poisson solver from convolution_kernel.cc to poisson.cc
* Fine-tuned deconvolution schemes for various running modes
* Added lots of doxygen documentation
* The DM transfer function is now deconvolved with the cell assignment
function in order to restore power near the Nyquist wavenumber.
* Added an option to change the random number sample cube size
[random]/cubesize. This should be set >128 to generate un-
correlated numbers. True fix pending.
* Removed some unused code
* Increased Buffer size for Gadget-2 output plug-in
