Override default fade-in / fade-out duration

[Xirt]

Currently, the fadeInMillis and fadeOutMillies are defaulted to the system animation times with no way to override them. I noticed a method has been implemented to provide this functionality, but the method is private and never called:

     * Set the duration of the fading in and fading out of the ShowcaseView
     */
    private void setFadeDurations(long fadeInMillis, long fadeOutMillis) {
        this.fadeInMillis = fadeInMillis;
        this.fadeOutMillis = fadeOutMillis;
    }

[Xirt]

Pull request #321 appears to fix this problem but has been pending since November last year. Maybe worth to merge this item as a quick fix?