Added missing error checking.
Removed useless tests.
Limit padding string to maximum block size.
Cleanup and padding optimisation.
Ensure counter goroutine is running.
Moved default counter implementation to main file.
Counter optimisation.

Using a simple mutex in the default counter instead of a gorouting/channel couple is much faster.
Don't use int64 when it's not necessary.
Added custom random and custom counter setters.
Added README