Clear validation empty non-required input

[wraithgar]

From issue #19

If a field has the required attribute set to false and you type something incorrect (invalid) in the input and try and submit the form it shows the error message, this is working fine. It is only when you then empty the input and and try and validate the form again the message will stay.
For example do this on the test from in the happy.js pack. Set the email required attribute to false and when you test leave the name field empty, then type an invalid email into the email input, submit the from, then remove the content from the email input and submit again.

The original issue ended up taking on a life of its own cause of a UI bug so I'm duplicating this here cause the original issue (don't clear validation errors on required elements simply cause the element was cleared and blurred) still stands IMO

[wraithgar]

Ok after fixing issue #19 this behavior does not seem to happen anymore. Yay!