Adding entries to X-MoneyTrace header

[HaloFour]

I'm working on some changes to the Scala Money library and I was looking at being able to propagate additional state about the span context across the Money headers. As the header is already a delimited set of name/value pairs it seemed like it would be fine to add additional values into the existing header:

X-MoneyTrace: trace-id=9121d79c-ce07-481e-b822-7f829bdd5186;parent-id=91877731;span-id=49430499;sampled=1;foo=bar

However I noticed that the Go implementation of money assumes that there can only be 3 key value pairs otherwise it fails to parse the header.

I was curious as to how much impact there could be in making this change to the X-MoneyTrace header (specifically how many Go services might be impacted due to requests coming from JVM-based services), and whether it might be possible to implement this change.

I've submitted a PR to implement this change: #44

@ptravers

[ptravers]

I think if you are going to move to a different header it should be the w3c header rather than continue with a separate money header