Modified card products in preparation for validation improvements.
* Removed defunct hipercard product;
* fixed matching regexes (re-based upon stripe's jQuery plugin);
* added validateLuhn indicator to each card product;
* added cardNumberLength array to each card product.
Rewrite of validation and rendering logic.
* Moves validation of card product details to the Skeuocard::CardProduct model.
* Shifts storage of validation state to input classes rather than trying to maintain internal state.
* Emits new events upon validation state changes.
* Skeuocard::FlipTabView now contains display state logic; observes card validation events.

* Fixed #21: "Valid class is being applied when fields aren't all filled."
* Fixed #62: "Month should accept a single number."
* Fixed #73: "Don't accept months over 12."
* Fixed #75: "cc_type not being updated."
* Fixed #57: "Underlying expiration date should allow use of month/year <selects>."
* Fixed #77: "Skeuocard + Jquery + jQuery.noConflict() &| Other Lib"
Removed unused issuers option.
Added isValid() method.
Updated README to reflect validation and API changes.
Merge branch 'feature/73-validation-fixes' into develop
Reworked number input handling code.
* Prevents non-numeric user input for card number (fixes #51);
* Allows FF users to tab out of card number fields (fixes #50);
* Allows basic use of DEL key (fixes #58);