Make each validation method callable by itself

[dhershman1]

The plan is to allow users to bring in and call validation methods they need/want

Example:
How it currently works

import simpleCard from 'simple-card';

simpleCard('4111111111111111'); // Validate single Card Number
simpleCard('333'); // Validate single CVN
simpleCard('1/20'); // Validate single date

Instead we should allow for:
Note The import from values are concepts/placeholders that may change on release

import validNumber from 'simple-card/number';
import validCVN from 'simple-card/cvn';
import validDate from 'simple-card/expire';

validNumber('4111111111111111');
validCVN('333');
validDate('1/20');