 increases or decreases the <code>step_size</code> of
the inner kernel based on the value of <code>log_accept_prob</code>. It is based on
equation 19 of Andrieu and Thoms (2008). Given enough steps and small
enough <code>adaptation_rate</code> the median of the distribution of the acceptance
probability will converge to the <code>target_accept_prob</code>. A good target
acceptance probability depends on the inner kernel. If this kernel is
<code>HamiltonianMonteCarlo</code>, then 0.6-0.9 is a good range to a