class Rcov::FileStatistics

considered executed if the the next statement was executed.
A comment is attached to the code following it (RDoc-style): it will be
a fraction, i.e. from 0 to 1.0.
Total coverage rate if comments are also considered "executable", given as

def total_coverage
  return 0 if @coverage.size == 0
  @coverage.inject(0.0) {|s,a| s + (a ? 1:0) } / @coverage.size
end