Since Postgres 9.6.8, at the top of the output of `pg_dump` it adds the line:
```sql
SELECT pg_catalog.set_config('search_path', '', false);
```
We must provide an absolute table reference to avoid errors when importing schema.sql.
Adds `dbmate dump` command to write the database schema to a file.
The intent is for this file to be checked in to the codebase, similar to Rails' `schema.rb` (or `structure.sql`) file. This allows developers to share a single file documenting the database schema, and makes it considerably easier to review PRs which add (or change) migrations.
The existing `up`, `migrate`, and `rollback` commands will automatically trigger a schema dump, unless `--no-dump-schema` is passed.
Closes https://github.com/amacneil/dbmate/issues/5
