Hardened the script with shellcheck + wget Improvement

Hi,

Here is a pull request for 2 things:

• Use Gitlab-CI for linting the script with shellcheck, to improve the code quality and avoid future problems
• Integrate the improvements of wget, proposed a long time ago by kaliko (Closes #2 ).

Kind regards,

Adrien

Signed-off-by: Adrien Grellier perso@adrieng.fr