SQL string template expansion support

[jadbox]

The NPM library postgres has a really nice feature to do string template expansions, can read about it here:
https://github.com/porsager/postgres

For example:

const users = await sql`
  select 
    * 
  from users
  where age in (${ [68, 75, 23] })
`

In theory, pgtyped, should be able to do something just like this too, and it would help with general ease of development.

[adelsz]

Unfortunately, this would make PG type inference impossible. Related #233