windows-iocp.cabal: reindent, and change summary to "Scalable and interruptible network I/O for Windows"

This reflects a change in direction for this project.  Originally, it was a
playground for me to experiment.  Now, I have a narrow focus:

 * Implement (almost [^1]) drop-in replacements for connect, accept, recv,
   and send that use IOCP.  This means use the network package, even though
   there are plenty of things I'd like to change.

 * Get it working on Windows Vista first, where CancelIoEx is available and
   I/O bound for a completion port isn't canceled on thread exit.
   Windows XP support is still crucial, but I don't want the I/O manager
   design to revolve around it.

 * Only support -threaded.  This means start actions can be in Haskell.
   Under the non-threaded RTS and Windows XP, to recv and send
   simultaneously, we would need to send I/O start actions to another OS
   thread, and such actions would need to be in C.

[^1]: I say "almost" because the caller will still have to associate the
      socket handle with the completion port.  Otherwise, attempting I/O
      will hang or something.
Make BOOL a newtype that shows as "TRUE" or "FALSE", and add fromBOOL and toBOOL
Throw IOError instead of WinError, and change "e_" to "e" in error code prefixes