Support more datatypes

[neurolabusc]

As noted here, this repo says to support dataypes 2,4,16 but does not. This can be observed with dragging and dropping the images of different datatypes from the niivue float32 (fslmean.nii.gz) and niivue-demo-images int16 (CT_Philips.nii.gz).

The solution is to add .buffer to read the bytes rather than convert them:

      case processedImage.DT_UNSIGNED_CHAR:
        processedImage.img = new Uint8Array(imageBytes);
        break;
      case processedImage.DT_SIGNED_SHORT:
        processedImage.img = new Int16Array(imageBytes.buffer);
        break;
      case processedImage.DT_FLOAT:
        processedImage.img = new Float32Array(imageBytes.buffer);
        break;
      case processedImage.DT_DOUBLE:
        throw "datatype " + processedImage.hdr.datatypeCode + " not supported";
      case processedImage.DT_RGB:
        processedImage.img = new Uint8Array(imageBytes.buffer);
        break;
      case processedImage.DT_UINT16:
        processedImage.img = new Uint16Array(imageBytes.buffer);
        break;
      case processedImage.DT_RGBA32:
        processedImage.img = new Uint8Array(imageBytes.buffer);
        break;
      default:
        throw "datatype " + processedImage.hdr.datatypeCode + " not supported";
    }