Added more library-like behaviour, updated README, updated examples

These were done:
 - **benford.rb updated**
  - added simple documentation
  - refactored a little
  - added library-like behaviour
  - added ascii_charts gem and additonal command line options
  - changed name of command line options (for better)
  - removed unnecessary code
 - **examples updated**
  - data.csv renamed to population_example.csv
  - the actual example is now in a seperate file called
    population_example.rb so benford.rb is just a file with a class in it
 - **README.md updated**
  - corrected spelling mistakes
  - added clearer examples (with options and without)
  - documented the new ascii_charts feature
  - covered command line options
  - covered dependencies
  - added additonal resources
  - beautified the file overall