Incompatible change to setopts

The setopts callback for probes was made asynchronous, and passes
the args (#exometer_entry{}, Options, NewStatus). A new module,
exometer_info.erl exports accessor functions (exprecs-style) to
facilitate access to record attributes without compile-time deps.

The reporter_setopts callback now receives the #exometer_entry{}
record again, since race conditions could result from fetching
it in the reporter process.