hist.py fails if it only receives the same number

``` shell
echo "2.718281828459045
2.718281828459045
2.718281828459045
2.718281828459045
2.718281828459045" | hist.py
```

outputs

```
Traceback (most recent call last):
File "/Users/bramp/bin/hist.py", line 151, in
main()
File "/Users/bramp/bin/hist.py", line 133, in main
hist = hist_fd(raw)
File "/Users/bramp/vendor/handy-tools/_hist.py", line 57, in hist_fd
return hist_dict(data, N = int(r / (2*iqr / math.pow(n, 1/3))))
ZeroDivisionError: float division by zero
```

Run the shell command from the issue, then inspect hist.py around main and vendor/handy-tools/_hist.py around hist_fd, the locations shown in the traceback. Confirm the behavior with repeated identical values and consider the task complete when the command finishes without the ZeroDivisionError and produces histogram output.

Written by the indexing model from the issue text.