add autoflake fixer (#3779)

* first attempt

* added autoflake executable

* added Windows executable for appveyor

* delete unused files

* corrected wrong sorting

supported-tools.md

@@ -408,6 +408,7 @@ formatting.
   * [purescript-language-server](https://github.com/nwolverson/purescript-language-server)
   * [purty](https://gitlab.com/joneshf/purty)
 * Python
+  * [autoflake](https://github.com/myint/autoflake)
   * [autoimport](https://lyz-code.github.io/autoimport/)
   * [autopep8](https://github.com/hhatto/autopep8)
   * [bandit](https://github.com/PyCQA/bandit) :warning: