Better relationship naming

[sheinbergon]

Changes

Fixes #377

Uses FK name for relationship names

Checklist

If this is a user-facing code change, like a bugfix or a new feature, please ensure that
you've fulfilled the following conditions (where applicable):

• You've added tests (in tests/) which would fail without your patch
• [] You've added a new changelog entry (in CHANGES.rst).

If this is a trivial change, like a typo fix or a code reformatting, then you can ignore
these instructions.

Updating the changelog

If there are no entries after the last release, use **UNRELEASED** as the version.
If, say, your patch fixes issue #123, the entry should look like this:

- Fix big bad boo-boo in task groups
  (`#123 <https://github.com/agronholm/sqlacodegen/issues/123>`_; PR by @yourgithubaccount)

If there's no issue linked, just link to your pull request instead by updating the
changelog after you've created the PR.

[coveralls]

coverage: 97.513% (+0.05%) from 97.459%
when pulling 76905c6 on sheinbergon:better-field-name-for-relationships
into b97ce66 on agronholm:master.

[agronholm]

I'll try to get this reviewed on Monday.

[agronholm]

One question and one trivial change.

[sheinbergon]

@agronholm whenever you have the time, please re-review my latest fixes

[agronholm]

Alright, looks good. I didn't go through this latest change with a fine-toothed comb, but it seems like a good bunch of improvements. We'll do further changes if we find a problem with it.

[sheinbergon]

Alright, looks good. I didn't go through this latest change with a fine-toothed comb, but it seems like a good bunch of improvements. We'll do further changes if we find a problem with it.

10x. I tidied up the code a bit. There's still an issue with collissions on M2O, But that'll be for a different PR