Add Split Parity: Need to add the Extended parity space with additional drives

[Smurf-IV]

11.0 2016/11

• Added support for splitting the parity in multiple partitions. You can now specify multiple files for a single parity. As soon a file cannot grow anymore, the next one starts growing.
  In the configuration file, just put more files in the same 'parity' line, separated by , (comma).
  Note that if this feature is used, the saved content file won't be read by older SnapRAID versions.