Support WC3 Trace Context format

[Knappek]

Jaeger supports W3C Trace Context Format according to the documentation about propagation format.

As far as I could see in the code this module only supports the Jaeger native format. As W3C Trace Context format seems to become the standard format for distributed tracing, it would be great to support it in this module as well, maybe make it optional to use.

Is that possible?

@kevinbader fyi.