* BENCHMARK_MAIN() now reports unrecognised command-line flags (see google/benchmark#320)
* add benchmark::ReportUnrecognizedArguments()
Update BENCHMARK_MAIN() to use ReportUnrecognizedArguments() instead of
having the reporting code directly in the macro.
See issue google/benchmark#320 for reference
* let's stick to american english -- fix type in ReportUnrecognizedArguments()
* make ReportUnrecognizedArguments() print to stderr
* make ReportUnrecognizedArguments() return true if any arguments have been reported (i.e. argc > 1)
