Recommend to make traceflags a struct

[bogdandrutu]

Right now TraceFlags is just a bit, I think it is more extensible to have it like a struct type TraceFlags byte and expose helpers like IsSampled on this struct.

[MrAlias]

The Go type system allows methods to be added to any types, not just structs, so I'm not sure that should motivate an underlying type change. That said, I think the downside of using a struct with the small increase in resource overhead might be outweighed by the potential extensibility.

What other fields do you anticipate being added to the TraceFlags type?