Added main property in package.json

Since the main chancejs library file is not named index.js or index.node (see http://nodejs.org/api/modules.html#modules_folders_as_modules ), this is needed so that the library can be found via require().
Add Luhn algorithm
Add basic credit card number generator
Add basic credit card types
Get cc type with associated data
Use cc_type() to generate cc_number()
Fix credit-card test
Rename `type` as `name` in  cc_types()
cc_type() can be filtered by name
cc_number() now obeys to type argument
Add more credit card types
Remove useless test
Changed cc_number() to cc()
Add short_name to cc_types(), allow specifying card type in cc() by that short_name as well