Pip-download

1. Add support for tzlocal>=3.0

1. add support for python3.9
2. code refactoring of tests

1. Add option "--show-urls“
2. Add support for tar.bz2 name resolution

1. fix bugs when create the config file at the first time
2. use monkey patch to alert the config file

- fix the docs

- You can use the config file to store your common used option now!
- All default values of the option `--python-versions` and `--platform-tags` have been cancled.
- Try to use the option `--show-config` to create the config file and add the json content which the keys of are "python-versions" and "platform tags" in the config file.