Fixed naming issues, added missing functionality, and added lua5.2 support.

* Added function host:destroy() for freeing up ports that a host is using.
* Added error handling for trying to work with a destroyed host. (Doesn't interfere with garbage collection.)
* Added lua5.2 support. I just used the compatibility module, it should work whether compiling for lua5.1 or lua5.2, but I'm not completely sure.
* Fixed awkward naming of socket_get_address (It now matches the rest of the lib as get_socket_address now). I feel like this is necessary because enet-lua doesn't have an ENetSocket type, so the naming doesn't make sense at all.

I may have made some unnecessary whitespace->tab changes because I used vim's retabbing functionality to  make sure everything was consistent to your coding style.