Add simple apl builder

[bahlo]

This adds a simple APL query builder. Example:

let query = QueryBuilder::new("my-dataset")
    .r#where("foo == 'bar'")
    .and("baz == 'qux'")
    .build();
assert_eq!(query, r#"['my-dataset'] | where foo == 'bar' and baz == 'qux'"#);