[feature] axel support for multithreaded downloads

CHANGELOG.md

@@ -29,6 +29,13 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
         <img src="https://raw.githubusercontent.com/vinifmor/bauh/staging/pictures/releases/0.9.4/arch_repo_mthread.png">
     </p>
 
+- Settings
+    - [axel](https://github.com/axel-download-accelerator/axel) added as an alternative multi-threaded download tool. The tool can be defined through the new field **Multi-threaded download tool** on the settings window **Advanced** tab
+    <p align="center">
+        <img src="https://raw.githubusercontent.com/vinifmor/bauh/staging/pictures/releases/0.9.4/mthread_tool.png">
+    </p>
+
+
 
 ### Improvements
 - Arch