this commit changes the way the plan is retrieved; implements Stringer on types.PlanExpression in preparation for HAVING support; removes last vestiges internal float64 arithmetic; implements a filter on PlanOpFilter; fixes various bugs in the PlanOptimizer when rewriting qualified references
* fixed selects with unqualified identifiers
* handle bad and non-existent query param inputs more appropriately
* added test coverage for PlanExpression Stringer
Co-authored-by: Matthew Jaffee <jaffee@pilosa.com>
