Parse adding a primary key as an alter table statement

I'm trying to parse a sizeable DDL script with the primary key detached in separate `alter table` statements
```
alter table MY_TABLE
   add constraint PK_MY_TABLE primary key (DATETIME, REGIONID)
      using index tablespace SOME_TABLE_SPACE;
```
I notice it picks up the additional indexes, but at the moment `simple-ddl-parser` does not pick up the primary key when it's added in this way.