Add error macro replacement section

[ryanthompson591]

We should add to section 8 a description of how to fire error tracking urls with macro replacement.

I suggest we add a new macro (this would be a SIVIC macro and not a VAST macro). SIVIC_ERROR_CODE

The section could read like this:

When firing error tracking pixels SIVIC errors should be of type 409 and SIVIC_ERROR_CODE should be replaced with the error code number.

For example:
If the player had the wrong SIVIC version (error code 1103) and the error tracking url was:
https://www.example.com/tracking?code=[ERRORCODE]&sivic_code=[SIVIC_ERROR_CODE]

Then the player would ping the tracking url:
https://www.example.com/tracking?code=409&sivic_code=1103

Note: 409 could be replaced with 902 if we can get that added to the VAST spec.

[ryanthompson591]

There is a suggestion to add to the VAST spec a generic INTERACTIVE_ERROR. This would require communication with the VAST working group.