Add Spookyhash code.

Add the code to Bob Jenkins' SpookyhashV2 to the repository. The code is
in public domain and available from:
(http://burtleburtle.net/bob/hash/spooky.html)
Fix Makefile.am to use Spookyhash code.
Change the code to use Spookyhash.

* This change removes the external dependency on OpenSSL, which should
  allow the code to compile on Mac OS X without specifying the
  MAC_OS_X_VERSION_MIN_REQUIRED non-sense.
* Spookyhash should be faster than SHA-1's Merkle-Damgård construction.
* Spookyhash is only 128-bits as opposed to SHA-1's 160-bits so memory
  consumption should be less. I doubt it will lead to too many
  collisions.
* The docs are updated to reflect the fact that OpenSSL is not a
  dependency.
Merge pull request #69 from sureshsundriyal/lnav-spooky

Replace SHA-1 with Spookyhash.