Add basic "values" functions to MarkLogicTemplate

[malteseduck]

Look to see if there are some simple (and generic) functions we could add to the template to enable easy pulling of index values. Ideally this would include aggregates as well, but for the simple case maybe just the values, potentially scoped by a structured query.

[malteseduck]

Have tried various ways to add it in to "make it easy", but none seem to "feel" right. As this is an "in-between" feature - not quite Spring Data, but I don't want to implemented a bunch of custom interfaces for ML functionality, maybe it should not be included.

[malteseduck]

Could be more of a "facets" set of functions, and there are many cases where wrapping this "pattern" in a function would help because it seems to be used a lot (i.e. shotgun joins), so will add to next release.