`r#` identifiers not working as column names

I was trying to name one of my table's columns `type`, but `r#type` causes the macro to panic.

```rs
proc-macro panicked: `"r#type"` is not a valid identifier
```

A minimal reproduction of the error can be created with

```rs
#[model]
#[table = "table_name"]
#[derive(Debug)]
pub struct MyTable {
    #[pk]
    id: String,

    r#type: MyTableType  // Enum defined with #[derive(FieldType)]
}
```