Support composite primary keys

It would be great if this module could support composite primary keys. For example:

key_column => [qw/key_1 key_2 key_3/];

I have a few tables I can't use this module for because they have composite primary keys. (I may be able to write a patch for this in the next week or so.)

The issue does not name a file or test; start by locating the module's current primary-key handling and database-table CRUD paths. Use the composite key_column array example as the starting requirement, and consider the work done when tables with composite primary keys are supported across the module's CRUD operations.

Written by the indexing model from the issue text.