Add core table record mod methods

[pydanny]

• [ ] insert
• [ ] delete
• [ ] upsert
• [ ] update

[jph00]

Also update, although that's not in the .py file -- sorry!

Note that all except delete should return the updated/inserted record (e.g. including auto-generated primary key).

[pydanny]

Fun complication, some of these methods already exist on SQLAlchemy Table classes for rendering of SQL statements. So we'll need to abstract things away an extra step.

[jph00]

Just need update and upsert now.

[jph00]

I changed my mind about upsert, since it's not widely enough supported. So we're done for the basics :)