Record is imported even if not using PostgreSQL

[HarrySky]

Currently in model.py Record is imported without checks in place whether user even have asyncpg installed:

ormar/ormar/models/model.py

Line 5 in 250f55a

from databases.backends.postgres import Record

It causes my app that use SQLite to crash with ModuleNotFoundError: No module named 'asyncpg'

One possible solution is to wrap it in try-except ModuleNotFoundError block, another - refactor check in Model.extract_prefixed_table_columns. Your thoughts?

It seems that tests are running with all backends and those kind of errors are not catched

[collerek]

Should be fixed in #24.
Please update to last version and check.

[HarrySky]

Yes, fixed, thanks a lot for quick patch 😄

I am experiencing other problems, will open issues in a moment