Added in the ability to split netmasks into smaller netmasks.

Hi,

At my work I was required to write some code that would programatically split netmasks (e.g to split 10.0.0/24 => ( 10.0.0.0/25 , 10.0.0.128/25) ) and to do this I extended your class and added a split method. 

In this pull request is the updated pm, pod and a new .t to test the split functionality. Feel free to use this if you feel that it is an appropriate addition to your class. It appears to work for all cases that I throw at it but I must admit that I don't quite understand or use some bits of the package ( e.g. storeNetblock or deleteNetblock ). I very well may have coded this in a way that is completely incompatible with some features or is distasteful to your general design and coding style; but I am very open to fixing this function if you give me a gentle nudge in the right direction. 

Regardless of whether you want to add this function or not, thank you very much for this distribution! it is very handy to me at work and I very much appreciate your efforts.

Cheers,
Ben Kolera