Add command line interface

[jez]

I wrote a simple command line wrapper for the core functionality.
It's especially useful for visualizing data from sources like
foo | sort | uniq -c.

Usage:
  bars [--width <n>] [--bar <char>] [--sort]

Input format:

  <count> <key>

  Provide data on stdin.
  Leading, trailing, or extra spaces in the middle are ignored.

Options:
  --width <n>   Restrict chart to <n> characters. [default: 60]
  --bar <char>  Use <char> to draw the bars. [default: #]
  --sort        Sort the list in descending order

Example:
  bars --width 40 --bar █ --sort < my-data.txt

Thanks building this! It's exactly what I was looking for.