makes value a derived property so that something extending this make it handle the very important usecase of being able to de-couple input value from produced value
dont show error messages for non-required inputs with tests until first blur
fix merge conflict
dont rely on changed property for validity class
Merge branch 'make-value-derived'
Merge pull request #21 from AmpersandJS/validity-class-doesnt-show

dont rely on changed property for validity class
merge master and fix conflicts
Merge pull request #20 from AmpersandJS/unrequired-with-test

Unrequired with test
fix merge conflicts; set starting value and input value to string on init