Issue: Threaded Upload

[abishekrsrikaanth]

@lian-yue, so far it has been quite fun working with this component but noticed two additional issues with simultaneous uploads. The current version I am on is 2.3.0-beta.2

1. So, let's say I have 10 files to upload and I set the thread to 4. When I initiate the upload, it uploads the first 4, but the next 4 starts only after the completion of the first 4. Is there a way to keep continuity, so if 2 on the first session gets uploaded, then it automatically starts 2 more. At any point, there will be 4 simultaneous uploads instead of 4 at a time. I hope that makes sense.

2. When I have the thread set to 4 and if I try to upload files less than 3, then file upload fails. If I upload 3 files then the upload works.

3. When the thread is set to 4 and if I upload 5 files, the first 4 files are upload and the last files get canceled. If I upload 4, all 4 are uploaded.

4. As a request, Can you make the retry as part of the component itself, that way it can be configured with props :retries="2" to configure how many times to retry the upload.