Add tiny integer field

[UnknownPlatypus]

I went for a tiny wrapper on top of SmallIntegerField, its convenient because we want the same implementation for a lot of hooks (db_check, cast_db_type, db_type_suffix) but currently, the validators hook is a bit incorrect because it uses SmallIntegerField ranges (-32768, 32767) instead of (-128, 127).

The ranges are stored on connection.ops.integer_field_range which makes them a bit difficult to change.
My only working idea for now would be to override validators with mostly the IntegerField.validators hook implementation, just altering the min/max values but it's not very clean and might drift.

Do you have a recommendation on how to solve this ?

Fixes #1121