Tracer.WithSpan() will now accept StartOptions as a variadic final parameter `opts`
that will be passed to the Tracer.Start() invocation that creates the Span
wrapping the user-provided function.
Change all occurrences of value to pointer receivers
Add meta sys files to .gitignore
Code cleanup e.g.
- Don't capitalize error statements
- Fix ignored errors
- Fix ambiguous variable naming
- Remove unnecessary type casting
- Use named params
Fix#306
* Make span start/end configuration more greppable
Rename SpanOption to StartOption
Rename StartOptions to StartConfig
Rename EndOptions to EndConfig
fixes#197
* move bridge out of the experimental directory
* drop a leftover from experimental stuff in gitignore
found by accident when doing `git grep experimental`.