Add test cases for HTML5 number input step attribute

The step attribute determines what values should be accepted by an HTML5
number input. If set to "any" or a floating point value, floating point
values should be permitted for the input by the validator.
Use `number` constraint for HTML5 number input if non-int step attribute

HTML5 number inputs allow floating-point numbers if the "step" attribute
is set to "any" or a floating-point number. In this case the appropriate
Parsley constraint would be "number".