PRs from postgres-ast-deparser for reference

[pyramation]

these should eventually be included in this library to have feature parity:

• Supports new nodes for deparser.insert_stmt() postgres-ast-deparser#11
• Add ast_helpers.raw_transaction postgres-ast-deparser#10
• Use native enum "ImportForeignSchemaType" postgres-ast-deparser#9
• Add deparser.import_foreign_schema_stmt postgres-ast-deparser#6
• #3 CreateStmt with tableElts postgres-ast-deparser#4