Schema support

It's possible to specify the schemas where the tables are located (if the database supports schemas).

_Example_

```sql
CREATE SCHEMA IF NOT EXISTS "test1";
CREATE TABLE IF NOT EXISTS test1.movies (
  id INTEGER PRIMARY KEY,
  title TEXT NOT NULL
);

CREATE SCHEMA IF NOT EXISTS "test2";
CREATE TABLE IF NOT EXISTS test2.users (
  id INTEGER PRIMARY KEY,
  title TEXT NOT NULL
);

Schemas must be specified in configuration. These are then automatically set in the postgres search path for the connection (see here for more info). Note that if we use schemas and migrations, we must specify the schema in the migrations table as well.

  ...
  "core": {
    "connectionString": "(...)",
    "schema": [
      "test1", "test2"
    ],
    "ignore": {
      "versions": true
    }
  },
  "migrations": {
    "dir": "migrations",
    "table": "test1.versions"
  },

  ...

danger

If two tables with the same name are present in different schemas, an error is thrown. Tables with the same name in different schema are not supported.