Add univariate elliptical slice sampler (#1109)
Add univariate elliptical slice sampler (#1109)

* allow ESS sampler on univar, per John Tipton suggestion

* minor (insignificant) changes to elliptical slice sampler ess

* upated ESS to handle univariate and multivariate nodes

* fixed ess sampler, using nimbleFunctionList for the mean

* change ess sampler to use model methods to try to avoid merge conflict with devel

Co-authored-by: Christopher Paciorek <cd2303627620d42aea1f002984decb2f80e8de9b@stat.berkeley.edu>
nimble-dev/nimble,nimble-dev/nimble,nimble-dev/nimble,nimble-dev/nimble,nimble-dev/nimble