update stdout trace with resource.

[rghetia]

This adds printing resources in the stdout exporter. The fix is not an elegant fix. resource.Resource fields are not exported. So instead of writing custom json.Marshal for entire SpanData I have wrapped it around an internal _SpanData containing original SpanData and the resources converted to a list of Attributes. _SpanData is then printed using standard json.Marshal.

[rghetia]

It might be better to convert Resource to Span Attributes on a copy of SpanData rather than the earlier solution of wrapping SpanData with another internal object. This is also inline with jaeger and zipkin (TBD).

@jmacd , @MrAlias WDYT?

[jmacd]

Yes, that sounds good.

[MrAlias]

Makes sense to merge with the attributes if that is the plan for Zipkin and Jaeger. Wondering about the Resource field in the SpandData, should we keep a copy of the Resource after merging? Seems a bit redundant, but also more accurate than an empty field.

[rghetia]

Makes sense to merge with the attributes if that is the plan for Zipkin and Jaeger. Wondering about the Resource field in the SpandData, should we keep a copy of the Resource after merging? Seems a bit redundant, but also more accurate than an empty field.

I'll remove it.