OpenTracing Shim: Add Tracer.Close() operation.

CHANGELOG.md

@@ -27,6 +27,8 @@ release.
 
 ### Compatibility
 
+- Add Tracer.Close() to the OpenTracing Shim layer.
+
 ### OpenTelemetry Protocol
 
 ### SDK Configuration

specification/compatibility/opentracing.md

@@ -12,6 +12,7 @@
   * [Start a new Span](#start-a-new-span)
   * [Inject](#inject)
   * [Extract](#extract)
+  * [Close](#close)
 * [Span Shim and SpanContext Shim relationship](#span-shim-and-spancontext-shim-relationship)
 * [Span Shim](#span-shim)
   * [Get Context](#get-context)
@@ -205,6 +206,12 @@ Errors MAY be raised if either the `Format` is not recognized
 or no value could be extracted, depending on the specific OpenTracing Language API
 (e.g. Go and Python do, but Java may not).
 
+## Close
+
+Optional operation. If this operation is implemented for a specific OpenTracing language,
+it MUST close the underlying `TracerProvider` if it implements a "closeable" interface or method;
+otherwise it MUST be defined as a no-op operation.
+
 ## Span Shim and SpanContext Shim relationship
 
 As per the OpenTracing Specification, the OpenTracing `SpanContext` Shim