appneta/oboe-ruby — pull request #67 by pglombardo (2014-08-05 12:55:17+00:00)
Title: Simplify start_trace by setting a default param

Currently we require `Oboe::API.start_trace` to pass a value for an X-Trace value. This is unneeded and can default to `nil`.

So calling `start_trace`without having an xtrace value will simply be called as:

```ruby
Oboe::API.start_trace('layer_name') do
# work
end
```