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

test_data/v0.1.1/schema.zipponschema

@@ -0,0 +1,10 @@
+User (
+  name: str,
+  age: int,
+  email: str,
+  bday: date,
+  last_order: datetime,
+  a_time: time,
+  scores: []int,
+  friends: []str,
+)