Duns.string() should have case sensitivity option

[br0r]

var schema = Duns.string().oneOf('asc', 'desc').caseInsensitive() // or .insensitive perhaps, or any other shorthand.

schema.validate('ASC') //True

[br0r]

If this is implemented, it should probably always do .toLowerCase on param values or something. At least it should be able to mix it with a string regexp.

Duns.string('Foo').match('foo').caseInsensitive().validate(); //True