Release v0.6.0

Initial Release.

Compatibility with the opentelemetry-go v0.6.0 release added for the following:

• exporters/metric/datadog
• exporters/metric/dogstatsd
• instrumentation/gin-gonic/gin
• instrumentation/go.mongodb.org/mongo-driver
• instrumentation/gorilla/mux
• instrumentation/labstack/echo
• instrumentation/macaron
• instrumentation/runtime