ClassicPress nightly builder

Copy example-config.sh to config.sh and fill in the values
- UPGRADE_API_SCRIPT should point to the v1-upgrade-generator/update.sh script from the https://github.com/ClassicPress/ClassicPress-APIs repo
Set full-build.sh to run as a cron job at midnight UTC (on a server that's using the UTC time zone, so that the build date is right)