Add support for include-pk

[J Kenneth King]

Defaults to false but when enabled in wal2json sends extra pk information:

 {                                                                                                            +
         "change": [                                                                                          +
                 {                                                                                            +
                         "kind": "insert",                                                                    +
                         "schema": "public",                                                                  +
                         "table": "w2j_pk_with_pk",                                                           +
                         "columnnames": ["a", "b", "c", "d", "e"],                                            +
                         "columntypes": ["int4", "timestamp", "text", "bool", "numeric"],                     +
                         "columnvalues": [123, "Sun Apr 26 16:23:59 2020", "Melanosuchus Niger", true, 4.560],+
                         "pk": {                                                                              +
                                 "pknames": ["b", "d", "e"],                                                  +
                                 "pktypes": ["timestamp", "bool", "numeric"]                                  +
                         }                                                                                    +
                 }                                                                                            +
         ]                                                                                                    +
 }