Add CLI class

[kazuooooo]

Hi, I added CLI class discussed in this issue

I make two cahnges.

• Extract OptionParser as class from command.rb
• Add CLI class which has run method

by these change, now can call command like

RailsBestPractices::CLI.run(['-d', '-o', 'path/to/file'])
# the same as "rails_best_practices -d -o path/to/file"

If some changes needed, I'm glad to do them :)