Permutation thresholding for the V'th most significant voxel.

[neurolabusc]

Mirman et al. (2017) suggest one may want to examine permute to detect the Vth most significant voxel. At the moment, NiiStat only computes the single strongest peak voxel (v = 1). NiiStat can be adapted to handle this. For example, for the Freedman-Lane analyses, the lines

    peak(p) = max(tp);
    nadir(p) = min(tp);

Can be rewritten

	%https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5826816/ 3. Continuous Permutation-Based FWER
	if ~exist('v','var')
		v = 1;
	end
	ranked_tp = sort(tp);
	peak(p) = ranked_tp(end-v+1);
	nadir(p) = ranked_tp(v);

Such that one can specify an arbitrary value of v.