Add error code atoms as #error.type

[mokele]

So that we don't have to put postgres error codes around our code and can use more sensible human readable versions.

[ates]

Good idea. It's similar to what I use in my own project. It would be good to have such code as a part of the epgsql.

[wg]

Thanks Mokele, and sorry for the delayed response. I've been back and forth on this one as changing the error record format isn't backwards compatible and I'm not keen on maintaining a list of error code mappings. So I'm going to close this request, but I'll keep it in mind for a 2.x release.