Node 0.11.x support

With these changes, node_mdns builds and runs under Node 0.11.14 and nan 1.3 although I cannot say with certainty as amount of testing it received with these changes is too little.
Better - At the top of the file:

````
#if (NODE_MODULE_VERSION <= 0x000B)
typedef InvocationCallback FunctionCallback
#endif
````
... and then use `FunctionCallback` in all signatures.