Break the fs package up into smaller parts.

The purpose of this is to make it easier to maintain and eventually to
allow the rclone backends to be re-used in other projects without
having to use the rclone configuration system.

The new code layout is documented in CONTRIBUTING.

fs/mimetype.go

@@ -0,0 +1,30 @@
+package fs
+
+import (
+	"mime"
+	"path"
+	"strings"
+)
+
+// MimeTypeFromName returns a guess at the mime type from the name
+func MimeTypeFromName(remote string) (mimeType string) {
+	mimeType = mime.TypeByExtension(path.Ext(remote))
+	if !strings.ContainsRune(mimeType, '/') {
+		mimeType = "application/octet-stream"
+	}
+	return mimeType
+}
+
+// MimeType returns the MimeType from the object, either by calling
+// the MimeTyper interface or using MimeTypeFromName
+func MimeType(o ObjectInfo) (mimeType string) {
+	// Read the MimeType from the optional interface if available
+	if do, ok := o.(MimeTyper); ok {
+		mimeType = do.MimeType()
+		// Debugf(o, "Read MimeType as %q", mimeType)
+		if mimeType != "" {
+			return mimeType
+		}
+	}
+	return MimeTypeFromName(o.Remote())
+}