Remove ExportComponent from README (#199)

* Remove ExportComponent from README

* Initial implementation of the OpenTracing bridge. (#197)

This is, where possible, a direct port of the current Java shim. There are some holes/TODOS. Notably:

-Missing the Binary injection/extraction of the span context. This doesn't exist with the current implementation of OpenTracing yet.
-Missing explicit timestamps for calls to OpenTracing ISpan::Log.
-Missing explicit timestamps for calls to OpenTracing ISpan::Finish
-Various calls to set/get baggage are not implemented. Requires OpenTelemetry DistributedContext to be finalized.

Other oddities worth nothing:

-The SpanBuilderShim has some conditional code for calling OpenTel SetCreateChild(true|false)
-The ScopeManagerShim is actively tracking scopes returned by calls to OpenTel WithSpan and associated those with the OpenTel ISpan used when calling WithSpan.

I tested this shim against an ASP.NET Core 3 Preview 8 service wired up with OpenTracing netcore and grpc collectors and exporting to Jaeger backend.

The included tests are unit tests only; no E2E tests.

README.md

@@ -132,12 +132,12 @@ Outgoing http calls to Redis made usign StackExchange.Redis library can be autom
 1. Install package to your project:
    [OpenTelemetry.Collector.StackExchangeRedis][OpenTelemetry-collect-stackexchange-redis-nuget-url]
 
-2. Make sure `ITracer`, `ISampler`, and `IExportComponent` registered in DI.
+2. Make sure `ITracer`, `ISampler`, and `ISpanExporter` registered in DI.
 
     ``` csharp
     services.AddSingleton<ITracer>(Tracing.Tracer);
     services.AddSingleton<ISampler>(Samplers.AlwaysSample);
-    services.AddSingleton<IExportComponent>(Tracing.ExportComponent);
+    services.AddSingleton<ISpanExporter>(Tracing.SpanExporter);
     ```
 
 3. Configure data collection singletons in ConfigureServices method:
@@ -187,7 +187,7 @@ var exporter = new JaegerExporter(
         AgentHost = host,
         AgentPort = port,
     },
-    Tracing.ExportComponent);
+    Tracing.SpanExporter);
 
 exporter.Start();
 
@@ -215,7 +215,7 @@ var exporter = new ZipkinTraceExporter(
     Endpoint = new Uri("https://<zipkin-server:9411>/api/v2/spans"),
     ServiceName = typeof(Program).Assembly.GetName().Name,
   },
-  Tracing.ExportComponent);
+  Tracing.SpanExporter);
 exporter.Start();
 
 var span = tracer
@@ -272,7 +272,7 @@ There is also a constructor for specifying path to the service account credentia
 ``` csharp
     var exporter = new StackdriverExporter(
         "YOUR-GOOGLE-PROJECT-ID",
-        Tracing.ExportComponent,
+        Tracing.SpanExporter,
         Stats.ViewManager);
     exporter.Start();
 ```
@@ -289,7 +289,7 @@ There is also a constructor for specifying path to the service account credentia
 ``` csharp
 var config = new TelemetryConfiguration("iKey")
 var exporter = new ApplicationInsightsExporter(
-    Tracing.ExportComponent,
+    Tracing.SpanExporter,
     Stats.ViewManager,
     config); // either global or local config can be used
 exporter.Start();