first prototype of the thumbnail service

Currently uses in memory caching and loads the file from the local
filesystem.

pkg/thumbnails/encoding.go

@@ -0,0 +1,47 @@
+package thumbnails
+
+import (
+	"image"
+	"image/jpeg"
+	"image/png"
+	"io"
+	"strings"
+)
+
+type Encoder interface {
+	Encode(io.Writer, image.Image) error
+	Types() []string
+}
+
+type PngEncoder struct{}
+
+func (e PngEncoder) Encode(w io.Writer, i image.Image) error {
+	return png.Encode(w, i)
+}
+
+func (e PngEncoder) Types() []string {
+	return []string{"png"}
+}
+
+type JpegEncoder struct{}
+
+func (e JpegEncoder) Encode(w io.Writer, i image.Image) error {
+	return jpeg.Encode(w, i, nil)
+}
+
+func (e JpegEncoder) Types() []string {
+	return []string{"jpeg", "jpg"}
+}
+
+func EncoderForType(fileType string) Encoder {
+	switch strings.ToLower(fileType) {
+	case "png":
+		return PngEncoder{}
+	case "jpg":
+		fallthrough
+	case "jpeg":
+		return JpegEncoder{}
+	default:
+		return nil
+	}
+}