rename Pair -> List
rename Arr -> Slice
	modified:   broom/builtin.go
	modified:   broom/builtin_test.go
	modified:   broom/core.brm
	modified:   broom/ea.go
	modified:   broom/object.go
	modified:   broom/pair.go
	modified:   broom/pair_test.go
	modified:   broom/read.go
	modified:   broom/read_test.go
	modified:   broom/repl.go
	modified:   broom/sf.go
	modified:   broom/sf_test.go
renamed pairImpl -> Pair
added methods as Sequence
	modified:   broom/pair.go