Cleaned up validToggler() and fixed PR problems

Added invalid class to validToggler
Prefixed valid and invalid with card-
Change CVC validation to use Card Type
Change remaining bullets to &bull
Validate Name and limit inputs to letters only (numbers on numpad still
allowed for alt + numpad special chars)

This reverts commit 433c598a.

This reverts commit 819b4991.

Added invalid class to validToggler
Prefixed valid and invalid with card-
Change CVC validation to use Card Type
Change remaining bullets to &bull
Validate Name and limit inputs to letters only (numbers on numpad still
allowed for alt + numpad special chars)

Fix validToggler() to correctly toggle on Expiry Date. Seems like
jquery.payment couldn't work with formatted date, as parsed by val.

switches to multiple input strategy where users pass in a selector that matches multiple fields, h/t to @joshlevinson

allows input selectors to be passed in as selectors or jQuery objects (fixes #30); provides better error messages when an input is not found (closes #32)