Features: clearDb by status, downloaded bytes in DownloadModel, Concurrent Limit ...

[ultranity]

Ketch have a nice kotlin style API and I do like it, but when trying I have found some missing features:

• DB management
  As it's a common demand to clear all canceled/finished task.
  for now we can use like:

                    ketch.getAllDownloads().filter { it.status == Status.SUCCESS }.forEach {
                        ketch.clearDb(it.id, false)
                    }

It will be cool to support clearDb by status to simplify the usage.

• DownloadModel info
  there are progress(maped in MapperUtil.kt) and totalBytes in DownloadModel, why not add also provide downloadedBytes?

• Concurrency
  Ketch mentioned it supports:"download multiple files in parallel", is there any way to control the concurrency?
  As Ketch use worker manager to queue download tasks instead of customized task queue, how to control the Concurrency/max items to download in parallel?

[khushpanchal]

1. I am planning to add support clearDb by status in future version. Feel free to create PR for this.
2. I thought it is not required and won't give much advantage, also if can be anyways calculated from progress and total bytes
3. Currently no way from outside to control concurrency. Currently max items are controlled by workmanager itself. Currently using CoroutineWorker that is controlling this as it is using Dispatches.Default. Will plan on it later. Feel free to create the PR for this as well.