SQL Migration query builder API and migration API

[christianparpart]

Refs #6

checklist (query builder)

each item should have its own test

• [x] CreateTable()
• [x] DropTable()
• [x] AlterTable()
• [ ] CreateTable: foreign keys
• [ ] AlterTable: foreign keys
• [x] AlterTable: RenameTable
• [x] AlterTable: RenameColumn
• [x] AlterTable: AddColumn
• [x] AlterTable: DropColumn
• [ ] AlterTable: AddIndex
• [ ] AlterTable: DropIndex
• [ ] AlterTable: ChangeColumn (to change type, or nullability)
• [x] make use of Migration query builder in existing tests to avoid writing raw CREATE TABLE statements.

based on that, we can build a DB migration API that makes use of the fluent API to express schema changes.