feat/user-templates (#9)

feat: user templates

pkg/invoice/resource.go

@@ -16,14 +16,16 @@ var DefaultOptions = Options{
 	IssueFilter: func(i *gitea.Issue) bool {
 		return i.Closed != nil && i.Closed.After(time.Now().AddDate(0, -1, 0))
 	},
+	CustomTemplate: "",
 }
 
 type Options struct {
-	Mindur      time.Duration
-	Since       time.Time
-	Before      time.Time
-	IssueState  gitea.StateType
-	IssueFilter func(i *gitea.Issue) bool
+	Mindur         time.Duration
+	Since          time.Time
+	Before         time.Time
+	IssueState     gitea.StateType
+	IssueFilter    func(i *gitea.Issue) bool
+	CustomTemplate string // if the length of the CustomTemplate is longer than 0, it get's used
 }
 
 type Repo struct {