Copies contents of the in-memory vault into a file-based vault.
The 'callback' parameter specifies a function which will be called when the operation completes (or an error is encountered). If the 'callback' parameter is not specified, then the method will block and will not return until the operation completes (or an error is encountered).
The callback for this method is defined as:
'err' is the error that occurred. If there was no error, then 'err' is 'null'.
'err' has 2 properties which hold detailed information:
This method saves the in-memory vault into the file specified by the FileName parameter.
The vault is saved "as is", with all parameters including encryption which were set for the in-memory vault.
Note: This method can only be called when Active is true, and cannot be called within events.