New step type for l.o.s. sampler:
  * Gaussian proposal for one distance bin in second half of
    reddening profile, to improve convergence at large distances.

Reorganizing burn in, main sampling phase for l.o.s. sampler:
  * Burn in and main sampling phase both use same number of steps.
  * In main sampling phase, 2/5 of steps use affine stretch.
    Remaining 3/5 use switch steps, mix steps and new type of step
    (move Delta in one distance bin).

L.o.s. sampler uses only 5 samplers per dimension, but 2000 steps per
sampler (from 20 sampler/dim, 300 steps/sampler).