func NewFloatValue(e expr.Expr, ts time.Time, val float64) Sequence {
	return NewValue(e, ts, expr.FloatParams(val), nil)
}
NewFloatValue makes a single-value sequence from a simple expression,
timestamp float value.
package encoding
import (
	"fmt"
	"math"
	"time"
	"github.com/getlantern/goexpr"
	"github.com/getlantern/golog"
	"github.com/getlantern/zenodb/expr"
)
var (
	log = golog.LoggerFor("zenodb.encoding")
)
type Sequence []byte
func NewSequence(width int, numPeriods int) Sequence {
	return make(Sequence, Width64bits+numPeriods*width)
}