message: allows ToneAudioBuffers to add a buffer which is not loaded
  also simplifies code a little
diff: @@ -5,7 +5,7 @@ import { noOp } from "../util/Interface";
  import { isString } from "../util/TypeCheck";
  import { ToneAudioBuffer } from "./ToneAudioBuffer";
  -interface ToneAudioBuffersUrlMap {
  +export interface ToneAudioBuffersUrlMap {
  [name: string]: string | AudioBuffer | ToneAudioBuffer;
  [name: number]: string | AudioBuffer | ToneAudioBuffer;
  }
  @@ -143,21 +143,14 @@ export class ToneAudioBuffers extends Tone {
  url: string | AudioBuffer | ToneAudioBuffer,
  callback: () => void = noOp,
  ): this {
  - if (url instanceof ToneAudioBuffer) {
  - this._buffers.set(name.toString(), url);
  - callback();
  - } else if (isAudioBuffer(url)) {
  - this._buffers.set(name.toString(), new ToneAudioBuffer(url));
  - callback();
  + if (url instanceof ToneAudioBuffer || isAudioBuffer(url)) {
  + this._buffers.set(name.toString(), new ToneAudioBuffer(url, callback));
  } else if (isString(url)) {
  this._buffers.set(name.toString(), new ToneAudioBuffer(this.baseUrl + url, callback));
  }
  return this;
  }
  - /**
  - * Clean up.
  - */
  dispose(): this {
  super.dispose();
  this._buffers.forEach(buffer => buffer.dispose());
  