* Unify API Span Start/End Options
Replace both with `SpanOption`. Add a unified `SpanConfig` to match and
a `SpanConfigure` function to parse a `SpanConfig` from `SpanOption`s.
Update all the related options to use new `SpanOption`s.
* No non-zero SpanConfig defaults
The SDK uses an internal clock for the current time that cannot be use
if it does not know the time has not been set.
* Append attributes for WithAttributes
This preserves existing behavior.
* Add unit test for SpanConfigure
* Propagate changes
* Update append option documentation
* Update testing comments
* Move comments on guarantees to appropriate function
* Add documentation for SDK methods
Include SDK implementation specific information in the Tracer Start
method and Span End method.
* Add changes to Changelog
* Apply suggestions from code review
Co-authored-by: ET <evantorrie@users.noreply.github.com>
* Update the SpanKind comment in the SpanConfig
Try for a less tautological comment.
Co-authored-by: ET <evantorrie@users.noreply.github.com>
