compile RANGE to an array containing the two values
hack for BETWEEN with new way of compiling RANGE; much nicer error with summary of args and annotations
Merge branch 'issue29' of file:///Users/moss/slamdata/ws3 into between
Merge branch 'prettify' into between

Conflicts:
	src/main/scala/slamdata/engine/physical/mongodb/planner.scala
working, but not yet complete or correct, implementation for BETWEEN
Merge branch 'master' of github.com:slamdata/slamengine into between
Merge branch 'master' of github.com:slamdata/slamengine into between
closer to a correct ExprOp for Between; no-op for Betwen in Pipeline phase
Merge branch 'master' of github.com:slamdata/slamengine into between
Merge branch 'master' of github.com:slamdata/slamengine into between
simplify Field phase with simple extractor
Clean up Selector phase with extractors (first pass)
more cleanup in Selector phase

IsArray extractor, defined along with the Array constructors
clean up pipeline phase, slightly

implement extractors for the remaining cases, and for object constructors
Merge branch 'master' of github.com:slamdata/slamengine into between
fix HasExpr
make the public names for LogicalPlan nodes just constructor/extractor objects
remove lower-case constructors in LogicalPlan
remove hardly-used LogicalPlan type aliases
implement "virtual functions" MakeObjectN and MakeArrayN