Misc changes

[james-callahan]

• Remove trailing whitespace
• Rename test/ to spec/ to follow busted convention
• Have :log_kv take an optional timestamp
• Add span:each_baggage_item()

[rnburn]

Most of those changes look good, but the other OT APIs don't have functions to lookup the tags and logs ... is there any reason we'd need them for Lua?

[james-callahan]

OT APIs don't have functions to lookup the tags and logs

It seems other languages have flirted with a get_tag:

• Remove Span.get_trace_attribute opentracing.io#47
• WIP: Span opentracing-rust#12

See opentracing/specification#12 for :each_baggage_item

[rnburn]

I see the discussion for tag accessors, but I checked the Go and Java APIs and don't see that any methods were ever added to the interface for them.

I'm fine with a function to iterate over the baggage -- that's pretty standard.

[james-callahan]

Rebased to have commits you're not sure about at the end (that way you can merge just the first commits if you want)

[rnburn]

I'm not sure how to do a partial merge like that. Could you just remove the get_tag, each_tag, and each_log functions? The other changes look good.

[james-callahan]

Done. once merged I'll send another PR for those bits.