Connection pool for PHP-FPM

Closes gh-21.
Also:
* Update/Fix tests
* php.ini: 'tarantool.persistent' and 'tarantool.con_per_host' flags.
* add 'tarantool.deauthorize' - for future uses (currently can't login
  back to guest)
* Update phpunit
* Add PMurHash.{c,h}, mhash.h (third_party)