Update jquery.number.js

Changelog:

* Added support for the delete key (and modified comments to differentiate between delete and backspace)
* Allow negative sign to be inserted at beginning of existing numbers
* Remove negative sign when value changes to "-0.00" (like when deleting the "1" in "-1.00")
* Don't remove negative sign when deleting numbers to the right of the decimal
* Allow more standard browser hotkeys like Ctrl+P, Ctrl+S, Ctrl+F, Ctrl+Z, F3, F5, F11, etc. within fields
* Properly initialize 'data.init' value when prepopulated via browser autofill or F5
* Consistent use of tabs for indenting code and consistent equality operators

Quickly tested in Firefox 32, Chrome 37, and IE 11 on Win7.
Merge pull request #62 from RichardDavies/master

Delete key support, browser hotkey improvement, and improved negative sign behaviour