allow hstore in query! macro

[ibotty]

With mytable as CREATE TABLE mytable(f HSTORE) the following query! invocation fails with
error: unsupported type hstore for param #1.

let query = query!(
    "INSERT INTO mytable(f) VALUE ($1);",
    PgHstore::new()
);

I assume that's because https://github.com/launchbadge/sqlx/blob/main/sqlx-postgres/src/type_checking.rs#L10-L213 does not contain PgHstore.

[abonander]

This should be pretty easy if someone wants to try their hand at it.

At its simplest, yes, it would just involve adding it to that list. Also Vec<PgHstore> | &[PgHstore] to support HSTORE[].

Actually testing that it works with the macros would be nice to have as well.