preliminary npreg + trees support, no gradients, no stderrors
nptgauss now computes various constants required for asymptotic errors
nptgauss automatically sets limits on b in accordance with available precision
added a maxima file which one can use to compute various kernels e.g.:

batchload("kernels.max")$
computeKernels(gaussian, inf)$

unfortunately maxima chokes on anything other than the second-order truncated gaussian at the moment.

trees + npksum are now exploited by npreg for a nice speed boost
gradients + trees + npreg remain unimplemented, but are next on the todo list