Update CHANGELOG

Use global tracer in README

`opentracing.GlobalTracer()` is more correct than `tracer`.

Correct spelling in comments

Merge pull request opentracing#108 from opentracing/bhs/spanlog

Introduce key-value Span logging as an RFC

Remove URL escaping from HTTPHeadersCarrier and add a test for it (op…

…entracing#113)

* Remove URL escaping from `HTTPHeadersCarrier` and add a test for it
* Support `HTTPHeaders` format in `MockTracer` with URL escaping
* Fix `go vet` complaints
* Add usage examples for `HTTPHeadersCarrier`

Merge pull request opentracing#110 from sebastianvera/master

Fix typo in `tracer.go`

Merge pull request opentracing#8 from opentracing/changes/split_tag_m…

…ap_out

split the trace tags out from the core context ID in marshal/unmarshal

Merge pull request opentracing#1 from opentracing/changes/rfc

DCP RFC