Fix negative zero

[johnjaylward]

Fixes #187 -0 now returns as a double.

[johnjaylward]

test cases submitted

[stleary]

What problem does this code solve?
Parser should follow the JSON spec and produce numeric values from '-0' and '-0.0'
This is a user-found defect. See issue #187.

Changes to the API?
XML.stringToValue(String) is deprecated in favor of JSONObject.stringToValue(String)

Changes to how the code behaves?
Negative zero strings are now parsed to Double instead of String.

Does it break the unit tests?
No, but new unit tests will be committed after this code is committed. See stleary/JSON-Java-unit-test#39.

Will this require a new release?
No, I am proposing for this change to be rolled into the next release. If you disagree, please
post in this thread

Should the documentation be updated?
No.

[johnjaylward]

-0 and -0.0 both parse to Double since Long/Integer would lose the sign.

[stleary]

Got it, thanks.

[coderextreme]

This fixed over 6300 instances in our JSON documents. Thanks everyone for the effort.