enum conversions

[Andrej Mitrovic]

Well I don't know about safety, but this will throw an exception at
runtime on invalid enum values, and it also seems to perform a little
better than your original classifyNumber function (The
classifyNumberNewImpl function is the new one):

http://codepad.org/qyUaD1Hj

I'm not sure what is making the code faster, but on my machine I get:
classifyNumberNew: 5543
classifyNumberOld: 5550