expose heuristic_name in report

[rafaelfranca]

We want to log reports grouped by heuristic, as there's nothing in Autotuner::Report::Base that allows us to determine that we added this simple field to copy across.

We want our report function to look like this:

Autotuner.reporter = proc do |report|
  Bugsnag.notify(Exception.new(report.heuristic_name)) do |payload|
    payload.add_tab(:autotuner, { report: report.to_s })
  end
end

Closes #11