Switching to automatic latest release builds

With this release, all other releases will be deprecated.
Please always pull the "master"-tag
Every two days master will compile the latest snapraid release on the latest alpine.
Also it will automatically do a make check.

Snapraid 12.1 with Apprise

This release uses Snapraid 12.1 with Apprise notifications instead of email.
BREAKING CHANGES
It uses a modified snapraid-runner.py with a new conf file.
All parts relating to the email notifications have been removed and replaced by Apprise.
See the README for examples of configuration.

Snapraid 12.1 + configurable cron job

Breaking Change: new environment variable - CRON_SCHEDULE=0 3 * * * is now required to set the cron job. If the variable is not defined, snapraid will not run automatically.

Snapraid v11.6

Stable baseline release
fetch latest alpine image, build snapraid with specified version and fetch latest snapraid-runner.