Requirements list (#3888)

* Initial list of packages in "lib" folder.

Table: https://gist.github.com/sharkykh/2f6aa19befbb8a503f8e335e54565046

* Read requirements.txt into setup.py install_requires

* bencode is now vanilla

* Badge, just for show

* Some formatting

* List changes from #3870

Update requirements.txt when merged.

* List fixes [skip ci]

* Fix package names: `fake-useragent`, `backports_abc`
* Fix `python-dateutil` version link
* Actual feedparser version is a commit hash

* Fix sorter (ignore chars when sorting)

* Update requirements file and list for latest changes [skip ci]

* Update sort.py

* Update sorting script to support VCS [ci skip]

* Update sort script and use it in setup.py [skip ci]

* Prepare for merge to develop [ci skip]

* Restore initial `install_requires`
* Change require.io badge to develop branch