quick question about writing datastore plugins, im very confused by this
```
DatastoreConfigParser() fsrepo.ConfigFromMap
```

there's functions like:
```
return func(params map[string]interface{}) (fsrepo.DatastoreConfig, error) {
```

1) how is the `map[string]interface{}` populated? i cant seem to find any ways of passing in the params
2)  `DatastoreConfigParser` only retutrns `fsrepo.DatastoreConfig` but no error, what happens with the error? does it get discarded?