Allow for maxlength of -1

-1 is a valid value for input maxlength (see: https://developer.mozilla.org/en-US/docs/HTML/Element/Input). When jQuery (1.5 at least, perhaps also in later versions) injects an input element into the DOM, Firefox (v20, OSX) sets the maxlength to -1 (unlimited). This caused maskMoney to think that the input was full because it was doing a > check on input.maxlength.

This change checks to see if the maxlength is set to -1 and allows that
Broaden the maxlength check to allow for any negative value

The specs say that any negative value is valid so we shouldn't check for just -1
Merge pull request #71 from gmoore/master

Allow maxlength using negative numbers
allow changing a number by selecting it even if maxlength is reached. fixes #70
improving readme adding info about read only fields
releasing maskmoney 2.1.2