Added ability to treatDashAsZero for numeric fields.

When config option treatDashAsZero is set to true, if formatFloat is called on "-" it will treat it as a number 0 instead of a string "-".

Sorry Mottie, I wasn't able to get the min.js to generate the same way you had.  

If there is anything else I can do, update documentation, etc, please let me know how I can help.