Changelog

Pending Release

Fixes #219 so that there is no longer a data race when reading and writing from spans

Thrift transport is eliminated
If no transport is specified, UseHTTP is now the default (was UseGRPC)
Requires go >= 1.7
Update to gogo-1.2.1, no longer using Google protobuf
Imports context via the standard library instead of golang.org/x/net/context
Fixes #182, so that StartSpan can now take SpanReferences to non-LightStep SpanContexts use
Adds experimental OpenCensus exporter
Access-Tokens are passed as headers to support improved load balancing
Support for custom TLS certificates.

Minor update to sendspan to make it easier to pick which transport protocol to use.
Add a new field to Options: DialOptions. These allow setting custom grpc dial options when using grpc.
- This is necessary to have customer balancers or interceptors.
- DialOptions shouldn't be set unless it is needed, it will default correctly.
Added a new field to Endpoint: Scheme. Scheme can be used to override the default schemes (http/https) or set a custom scheme (for grpc).
- This is necessary for using custom grpc resolvers.
- If callers are using struct construction without field names (i.e. Endpoint{"host", port, ...}), they will need to add a new field (scheme = "").
- Scheme shouldn't be set unless it needs to overridden, it will default correctly.

Adds compatibility for io.Writer and io.Reader in Inject/Extract, as required by Open Tracing.

We are replacing the internal diagnostic logging with a more flexible “Event” framework. This enables you to track and understand tracer problems with metrics and logging tools of your choice.
We are also changed the types of the Close() and Flush() methods to take a context parameter to support cancellation. These changes are not backwards compatible and you will need to update your instrumentation. We are providing a NewTracerv0_14() method that is a drop-in replacement for the previous version.