Add MinGW to our Continuous Integration. (JSBSim-Team#283)

This new target builds and tests JSBSim with the MinGW32 platform.
The compilation of the Python module is disabled for now.

Release files built by GitHub Actions

This is WIP, do not discard Travis and AppVeyor yet !

Release files built by GitHub Actions

This is WIP, do not discard Travis and AppVeyor yet !

Fixed the branch name in AppVeyor.

Updated release to 2019 (issues JSBSim-Team#166 and JSBSim-Team#69). (J…

…SBSim-Team#175)

Make Travis deploy Debian packages under a unique ID/tag.