Allow handlers to return values

Hello,

As mentioned in my original issue - #62 , I'm interested in allowing handlers to return values.

This is the change I'm currently using.  As you'll see it's literally a single line.  Hardly worth claiming a spot in the package.json, but I think will be helpful for people looking to return promises or using handlers in other ways.

I ran your mocha tests and it looked clean.  I wasn't sure if you wanted tests added, but honestly my experience with mocha is very limited.  I did try things with various handler values though (function, string, "*", undefined) and got the expected results.  

Anyway, thanks for considering this and no rush.

-James