* 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
