Feat: another API like ContinueFromRequest but allow parameter (not http.Request)

[yeqown]

Summary

another API like ContinueFromRequest but allow a different parameter (not http.Request)

Motivation

support trace information transfer across process bwtween different protocols

Additional Context

maybe looks like:

func ContinueFromXXXX(trace string) SpanOption {
	return func(s *Span) {
		if trace == "" {
                        return
                 }
		s.updateFromSentryTrace([]byte(trace))
	}
}

[yeqown]

For example, in this issue #240:

• how to extract trace info from request?
• how to inject trace info into context.Context

[cleptric]

Fixed in v0.14.0 via #434