Tango.info musical work code

The work_codes are not stable (yet), they are sometimes changed. Once they were planned to be 6 letter mnemonic. There are lot of codes still starting with zz and some have more than 3 numbers in it.

Current policy aims to have at least 4 letter and only 2 numbers. This is easier to achieve than 6 numbers : T.i editor can drag drop in Excel (automatic filling and increasing number) to get new codes.

In a good DB one would probably have a simple numeric work_id. work_id could be implemented additionally.