Go bob walker, go!

Port bob walker to Go.

bob walker retains his existing functionality in Go, with the exception
that he doesn't take cumulative command-line arguments, i.e.:

Invalid:
```
go run bob-walker.go -sd
```

Valid:
```
go run bob-walker.go -s -d
```
Concurrent bob walkers!*

* Admittedly a contrived use of Goroutines
bob may time out when sleeping

bob gets sleepy in drunk mode.

Sleep duration calculated using a random integer following the example
in:
http://golang.org/pkg/time/#Duration
Add turbo bob

Turbo mode means bob walker can not only be concurrent, he's also
parallelised on multi-processor systems[1].

[1]: http://www.youtube.com/watch?v=cN_DpYBzKso
Sort command-line options alphabetically

Sort command-line options alphabetically.

Except for the case statement, where we keep `-h` separate since it's
functionally different, i.e. not a mode.