detect `db` field

[tristanwietsma]

If a db field exists, build I/O methods.

[tristanwietsma]

• general database I/O
  • create the table
  • drop the table
  • insert a row
  • select a row
• operations on the current struct
  • delete (use the primary key)
  • get/load/fetch (accept the primary key and assign result to the caller)