Added more library-like behaviour, updated README, updated examples, added ascii_charts feature (as discussed in issue #3)

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
 - **possible future additions**
  - tests (woho!)
  - more examples (on larger datasets maybe?)
  - better graphs and charts (more detail)
  - refactor more (the DRY rule is broken in the `Benford#draw_percentage` and `Benford#draw_log_percentage` methods!)