Support for UUID key column

[erezsh]

Currently only working for MySQL, but I'm posting it for comments about my approach and choices.

Next steps would be to -

• Add more tests. Maybe into test_database_types

• Support more databases and column types.

[sirupsen]

Nice! This is a really elegant implementation. The direction definitely looks good to me

Would love to see those type tests you mentioned in the opening description to make sure it behaves. Probably we can have a UUIDFaker or something. We might need both a "string" and "uuid" type category to test this there?

[sirupsen]

Based on the replies to comments, whenever you've made the changes you find appropriate to address them, go for it 👍🏻

[erezsh]

@sirupsen This PR is ready. I added a few more changes, but nothing too surprising.

Still, thought I'd give you a chance to review it.

[sirupsen]

Looking good Erez!! Let's get them to check this out in the issue!

Only some small comments that I'll leave at your discretion, won't need to look again