Move trace api package into otel

[MrAlias]

Move the api/trace package into the otel with the following changes:

• trace.ID has been renamed to otel.TraceID.
• trace.IDFromHex has been renamed to otel.TraceIDFromHex
• trace.EmptySpanContext is removed to reduce the package contents and maintenance burden and the simplicity to duplicate the functionality it provided.
• The package documentation has been updated.
• The ErrorOption has been changed to an interface to conform with the project design guidelines which included adding a NewErrorConfig function.

The api/trace/tracetest package is moved to otel/oteltest.

Part of #964 and #1179

[codecov]

Codecov Report

Merging #1229 into master will increase coverage by 0.2%.
The diff coverage is 80.4%.

@@           Coverage Diff            @@
##           master   #1229     +/-   ##
========================================
+ Coverage    76.6%   76.9%   +0.2%     
========================================
  Files         133     130      -3     
  Lines        5754    5761      +7     
========================================
+ Hits         4412    4433     +21     
+ Misses       1093    1079     -14     
  Partials      249     249             

Impacted Files	Coverage Δ
api/global/internal/state.go	81.8% <ø> (ø)
api/global/internal/trace.go	88.8% <ø> (ø)
api/global/trace.go	66.6% <ø> (ø)
bridge/opentracing/util.go	100.0% <ø> (ø)
exporters/stdout/exporter.go	25.9% <ø> (ø)
oteltest/mock_span.go	12.5% <0.0%> (ø)
sdk/trace/sampling.go	100.0% <ø> (ø)
internal/trace/parent/parent.go	21.0% <40.0%> (ø)
propagators/trace_context.go	65.5% <52.3%> (ø)
trace_noop.go	53.3% <53.3%> (ø)
... and 22 more

[louiemiranda]

This has broke https://github.com/go-redis/redis

../../../github.com/go-redis/redis/internal/util.go:10:2: cannot find package "go.opentelemetry.io/otel/api/trace" in any of: /usr/local/Cellar/go/1.13/libexec/src/go.opentelemetry.io/otel/api/trace (from $GOROOT) /Users/louie/go/src/go.opentelemetry.io/otel/api/trace (from $GOPATH)

[Aneurysm9]

This has broke https://github.com/go-redis/redis

../../../github.com/go-redis/redis/internal/util.go:10:2: cannot find package "go.opentelemetry.io/otel/api/trace" in any of: /usr/local/Cellar/go/1.13/libexec/src/go.opentelemetry.io/otel/api/trace (from $GOROOT) /Users/louie/go/src/go.opentelemetry.io/otel/api/trace (from $GOPATH)

It hasn't. Please ensure that you are using Go in module mode. That is the default in 1.14+, which is all that is currently supported by this project. When using Go in module mode the go.mod in the go-redis module will instruct Go to use v0.11.0 which has all of the packages in the place go-redis expects to find them.