feat(eventstore): sdk (#39)

* sdk

* fix(sdk): return correct error type

* AppendEventError instead of Aggregater error

* fix(tests): tests

* fix(tests): wantErr to is error func

internal/eventstore/models/aggregate.go

@@ -24,11 +24,8 @@ type Aggregate struct {
 	editorUser    string
 	resourceOwner string
 	Events        []*Event
-	Appender      appender
 }
 
-type appender func(...*Event)
-
 func (a *Aggregate) AppendEvent(typ EventType, payload interface{}) (*Aggregate, error) {
 	if string(typ) == "" {
 		return a, errors.ThrowInvalidArgument(nil, "MODEL-TGoCb", "no event type")
@@ -81,8 +78,3 @@ func (a *Aggregate) Validate() error {
 
 	return nil
 }
-
-func (a *Aggregate) SetAppender(appendFn appender) *Aggregate {
-	a.Appender = appendFn
-	return a
-}