Added Windows port (see #233)

PR to add support for Windows (see #233).

You'll need MinGW to compile and install Readline from [GnuWin32](http://gnuwin32.sourceforge.net/packages/readline.htm) and libmmap from [mman-win32](https://code.google.com/p/mman-win32/). I've also dropped the sockets support because it's really ugly to adapt it to `winsock2.h`.