Compound keys aren't handled

At minimum, it appears the `***FIXME***` code is reached when a logical decoding event is generated for a table with a compound index for its primary key.

Here is the DDL for a table that triggers this condition:

``` sql
CREATE TABLE assesses
(
    student_id INTEGER NOT NULL,
    sparkpoint_id CHAR(8) NOT NULL,
    reflection TEXT,
    PRIMARY KEY (student_id, sparkpoint_id)
);
```
