Move Windows port to MinGW

- Add calls to WSAStartup in the network code as required by
  Winsock.
- Add Windows-specific init_random_state function which uses the
  Crypto API.
- Move Windows port to MinGW and update build system to create a
  64-bit binary by default.
- Install text files as .rtf so they won't open in Notepad by default
  (Wordpad understands Unix line endings; Notepad doesn't).
- Simplify WiX installer code.

Signed-off-by: Jens Axboe <axboe@kernel.dk>