Rename header from Correlation-Context to correlationcontext

[mwear]

The reason for this change is to make the header interoperable with non-HTTP protocols that may have more restrictions on header naming than HTTP. This follows the conventions used for the trace context headers: traceparent and tracestate.

See #13 for more discussion.

[iredelmeier]

Alternative suggestion: correlations, as this would eliminate potential punctuation concerns.

[SergeyKanzhelev]

In OpenTelemetry it will be called Distributed Context. If we are making a change we can do a bigger change and need to re-visit the name.

I like Correlation-Context from the perspective that is already working in .NET and some people picking it up. See the presentation on recent observability summit. So we need to weight benefits of dashless name (which I do not question) and the landscape of existing implementations.

[SergeyKanzhelev]

I'm blocking PR for more discussions

[SergeyKanzhelev]

@bogdandrutu there was a discussion about the tradeoff this decision brings. Please see in #13. Do you believe the benefits of dash-less name worth the change?

[danielkhan]

Eventually we agreed on naming the header 'baggage'. Closing this one.