Add a CHANGELOG file

[tedsuo]

In the same manner as the golang changelog: https://github.com/opentracing/opentracing-go/blob/master/CHANGELOG.md

[coveralls]

Coverage remained the same at 81.515% when pulling a47aa44 on tedsuo/add-changelog into 242ba95 on master.

[pavolloffay]

Could be used the same formatting symbols as in other markdown files in this repository. e.g. # for headers, * for lists

[tedsuo]

I was trying to be uniform by copying the style in the go CHANGELOG ;) : https://raw.githubusercontent.com/opentracing/opentracing-go/master/CHANGELOG.md\

We also use .rst instead of .md in some repos. 🤷‍♂️

I prefer # and * so I'll switch to that. Maybe we can standardize and change the others as part of the upcoming "language maintainer" initiative.

[pavolloffay]

Could we add one list item per added change? All the following would be in the one list item. Also, add a link to the PR, in some projects there is also a name of the commiter.

Two major changes are missing there:

• introduction of log fields
• removed span.log(object) methods

[tedsuo]

I'm not sure what you mean by "All the following would be in the one list item." Do you mean only one list item for all the Scope/ActiveSpan changes?

[pavolloffay]

Yes as it was part of one PR

[tedsuo]

I looked though the PRs... unfortunately I don't think the Pull Requests line up cleanly, as we went through many revisions. I will try to find a middle ground.

[carlosalberto]

Nice! Besides Pavol's remarks, I'd also mention that:

• We have deprecated startManual() in favor of start().
• Added an examples directory.
• Maybeeee mention MockTracer uses TEXT_MAP as its default propagator, and added multi support reference.

[yurishkuro]

should we adopt the http://keepachangelog.com/en/1.0.0/ format?

[tedsuo]

@yurishkuro http://keepachangelog.com/en/1.0.0/ seems nice but I'd like to get a language maintainer group together to start making these decisions. There's a set of things we should standardize on, such as PR/Issue templates, release procedures, etc...

[tedsuo]

@pavolloffay @carlosalberto @yurishkuro I updated this PR, sorry for the delay.

• Switched to more standard markdown syntax.
• The PRs in the v0.31 were too messy to reference, as a result of numerous revisions, so I did not include them.
• We could include a link to the tracking issue, but I'm not sure how helpful that is (0.31.0 Release Candidate #189)
• Instead I simplified the line items to objects which were added and removed from the core API, and method changes on the Tracer object. Hopefully that's the right level of detail.

[yurishkuro]

LGTM. Were there any other minor API changes, like in the tags?

[pavolloffay]

LGTM, although at least one minor yet important thing is missing. Removed log.(Object) methods.

[pavolloffay]

I will merge this and open subsequent PR to add more links in there.