Add function calcMetrics_bisect() that is specifically for computing the bisected variograms with vario_bisect(). Change calcMetrics() back to using vario().
Annotate sorExp() and jacExp() so it is clear these functions generate the expected value for binary similarity indices rather than abundance-based indices.
Refactor null.perms() to have a more readable code style.
Refactor null.perms() with additional style changes and improved function generality.  Small change to vario_bisect() to make it more consistent with vario().
Create the function random_shuffle() which is a more streamlined version of null.perms() that is only used for generating completely randomly shuffled community variograms.