This is one possible "fix" to #168. With this we can `catListTable` arbitrarily deep trees of `ListTable`s.
It comes at a relatively high cost, however.
Currently we represent nested arrays with anonymous records. This works reasonably well, except that we can't extract the field from the anonymous record when we need it (PostgreSQL [theoretically](https://www.postgresql.org/docs/13/release-13.html#id-1.11.6.16.5.6) suports `.f1` syntax since PG13 but it only works in very limited situations). But it does mean we can decode the results using Hasql's binary decoders, and ordering works how we expect ('array[row(array[9])] < array[row(array[10])]'.
What this PR does is instead represent nested arrays as text. To be able to decode this, we need each 'DBType' to supply a text parser in addition to a binary decoder. It also means that ordering is no longer intuitive, because `array[array[9]::text] > array[array[10]::text]`. However, it does mean we can nest `catListTable`s to our heart's content and it will always just work.
Types in PostgreSQL can also be qualified with a schema. However, it's not sufficient to just change the type of `TypeInformation`'s `typeName` to `QualifiedName`, because a type isn't *just* a name. Postgres types can also be parameterised by modifiers (e.g., `numeric(7, 2)`) and array types of arbitrary depth (e.g., `int4[][]`).
To accomodate this, a new type is introduced, `TypeName`. Like `QualifiedName`, it has an `IsString` instance, so the common case (`schema` set to `Nothing`, no modifiers, scalar type) will continue working as before.
This does away with the weird variadic arguments thing we had going on with `function`.
Functions with no arguments are now written as:
```haskell
now :: Expr UTCTime
now = function "now" ()
```
Functions with multiple arguments are now written as:
```haskell
quot :: Sql DBIntegral a => Expr a -> Expr a -> Expr a
quot n d = function "div" (n, d)
```
Single-argument functions are written exactly as before.
This adds a new type `QualifiedName` for named PostgreSQL objects (tables, views, functions and sequences) that can optionally be qualified by a schema. Previously only `TableSchema` could be qualified in this way.
`QualifiedName` has an `IsString` instance so the common case (where the schema is `Nothing`) doesn't have to care about schemas (if `OverloadedStrings` is enabled).
This also refactors `TableSchema` to use `QualifiedName` for its `name` field and drops its `schema` field.
Thanks to @elldritch for the bug report and the inspiration.
