This introduces:
* an explicit check for the existence of the latest version tag
* This way, we don't need to bother to have `nightly` or `dev` tags in place. The new check works by `curl` failing, if the target tag does not exist.
* more verbose output
* This was just for debugging actually, but I believe it might help in the future.
* input parameters to the `build.sh` script
* This allows for using the script also from other repos. I'd like to keep trying things without having to ask you for checking in Drone.io...
