BETWEEN, a more mature approach

This is a work in progress.

`RANGE` is now compiled to construct an array of values.

`Between` is now handled as follows in the planner phases:
1. an `ExprOp` is constructed, but not yet used (not the correct one yet; there will be some work to represent all the expressions we support as exprOps, but I believe everything is in place to do this work). This expression will eventually be used to translate portions of the expression to JS for use with `$where`.
2. a `Selector.And` instance is constructed which is actually used.
3. the pipeline phase has a case for `Between` so as not to fail, but does nothing interesting with it. Not sure what we actually need there, if anything.
Did you change `Range` into a virtualized function that compiles to `MakeArrayN(min, max)`? If so it'll be constructed in the pipeline phase, not the expr op phase. The expr op phase will stop producing annotations after `min` and `max` (i.e. nothing higher in that subtree will contain an expr annotation). Then the `Between` can be dealt with explicitly in the pipeline phase.