Currently, if a sql row read needs to be deserialized into a
struct, and the struct has one of the fields as a Rust enum
type, then the deserialization fails. For example:

```rust
struct MyRow {
  id: i32,
  status: Status
}

enum Status {
  Pass,
  Fail
}

```
The deserialization of a row: `1, 'Pass'` will fail.

This commit adds the ability to deserialize a RowValue into
an Enum type.