Release 0.0.1

Add more test coverage for base64 encoding/decoding.

Fix bug in LookupKey.

lightstep-tracer-c++-0.5.0

Use Carrier.LookupKey if available for single key propagation.

Avoid unnecessary copying when propagating.

Run clang-format.

Fix missing protobuf flags.

Support overriding OPENTRACING_INCLUDE_DIR and OPENTRACING_LIBRARY

Add flags for when using protoc.