allow speed from get (#383)

* allow speed from get

* updating the version to use effor param in libvips

options.go

@@ -44,6 +44,7 @@ type ImageOptions struct {
 	Color         []uint8
 	Background    []uint8
 	Interlace     bool
+	Speed         int
 	Extend        bimg.Extend
 	Gravity       bimg.Gravity
 	Colorspace    bimg.Interpretation
@@ -144,6 +145,7 @@ func BimgOptions(o ImageOptions) bimg.Options {
 		Rotate:         bimg.Angle(o.Rotate),
 		Interlace:      o.Interlace,
 		Palette:        o.Palette,
+		Speed:          o.Speed,
 	}
 
 	if len(o.Background) != 0 {

params.go

@@ -56,6 +56,7 @@ var paramTypeCoercions = map[string]Coercion{
 	"interlace":   coerceInterlace,
 	"aspectratio": coerceAspectRatio,
 	"palette":     coercePalette,
+	"speed":       coerceSpeed,
 }
 
 func coerceTypeInt(param interface{}) (int, error) {
@@ -350,6 +351,11 @@ func coercePalette(io *ImageOptions, param interface{}) (err error) {
 	return err
 }
 
+func coerceSpeed(io *ImageOptions, param interface{}) (err error) {
+	io.Speed, err = coerceTypeInt(param)
+	return err
+}
+
 func buildParamsFromOperation(op PipelineOperation) (ImageOptions, error) {
 	var options ImageOptions