Automatically retrieve latest version?

[M5oul]

As done on YunoHost-Apps/cesium_ynh#3.

[M5oul]

I think versions should stay on stable and major ones.
If there is a critical bug fix, the version should be updated.

[M5oul]

Ok, finally, It's annoying to manually update that version number.
Let's automatically update that version number.
Duniter releases are generally stable and do not change the package. Tests are not more necessary.
What I wanted was to avoid that the install fail because the package do not exist, for instance for the ARM the package.
I finally found a way to retrieve last version for ARM or x64 which isn't necessary last version.
That way, the script won't fail.
Finally, I think all this works could have been avoided with a Debian repository.