Add support for user functions (#608)

* Add initial support for functions
* Show functions definitions
* Fix client tests
* Fix schema objects search
* Perform partial matching for functions
* Add function test
* Make sure to close client connections so that database could be dropped in tests
* Fix lint
* Allow to copy the view/functions definitions
* Nits

pkg/client/client.go

@@ -197,6 +197,10 @@ func (client *Client) MaterializedView(name string) (*Result, error) {
 	return client.query(statements.MaterializedView, name)
 }
 
+func (client *Client) Function(id string) (*Result, error) {
+	return client.query(statements.Function, id)
+}
+
 func (client *Client) TableRows(table string, opts RowsOptions) (*Result, error) {
 	schema, table := getSchemaAndTable(table)
 	sql := fmt.Sprintf(`SELECT * FROM "%s"."%s"`, schema, table)