Redshift can be accessed and `up`/`down` SQL executed with the `pq`
library by default, however, the `createVersionTableSql` of the `PostgresDialect`
is not compatible with Redshift due to the `serial` datatype and `now()` default on.
This PR creates a new Redshift dialect. The dialect still uses the `pq` library and
only updates the SQL in `createVersionTableSql` to be compatible with Redshift.
Closes#32.