Date, clean and errors

Added the datatype date, time and datetime

Moved all custom erros to a single file

Cleaned code to be more readable and created some small utils

Other stuffs that I dont recall. Basically preparing for the
relationship implementation

example.zipponschema

@@ -2,6 +2,9 @@ User (
   name: str,
   age: int,
   email: str,
+  bday: date,
+  last_order: datetime,
+  a_time: time,
   scores: []int,
   friends: []str,
 )