Use RWMutex for stats variables locking.
Add missing mutex lock in PrintProgress().
PrintOutput() code optimizations.
Ignore duplicates in server list.
Print header, footer and progress to stderr instead of stdout.
Removed commented out variable and command line parameter.
Code processed with gofmt.
Removed logfile command line argument.
Removed obsolete function argument for Command().
Use template strings for command output.
Disable colors when output is piped to a file.
Print errors to stderr instead of stdout.
Version increased.