Use the lazy evaluation for the Base class
Loop through validate numbers to check them
Rename number to number_to_validate
Make the internal methods and variables more sementic
Rename the .double_odd_numbers to .double_digit_on_even_position
DRY up the Base class
Remove note
Change the description for .double_digit_on_even_position
Keep on refactoring
Add .check_digit method
Cache the checksum
Remove the :check_digit attr
Add requirements to number_to_validate
DRY up
Whitespace and DRY up
Rewrite the README, now that were using a different calculation