**Backward incompatible change**
* In the migration yaml file, the ``command`` and ``command_args`` options are
now all merged into ``command``
**Features**
* Backup command and backup's ignore_if are now run in a 'sh' shell so we can
inject environment variables in the commands
* Backup command can now use ``$database``, ``$db_host``, ``$db_port``,
``$db_user``, ``$db_password`` that will be substituted by the current
configuration values
**Bugfixes**
* When starting 2 concurrent marabunta process and the first fail, it releases
the lock and the second would start odoo without actually run the migration.
Now, when the migration lock is released, the other process(es) will recheck
all versions as well before running odoo.
**Documentation**
* Add some high-level documentation