Add UNIX socket support

[rybakit]

E.g.:

$t = new Tarantool('unix:///tmp/tnt.sock');

Socket URI format: http://php.net/manual/en/transports.unix.php

[bigbes]

It'll be added in PHP7 branch, since it needs refactoring of API.

[Totktonada]

See https://github.com/bigbes/tarantool-php/commits/php7-v2

[rybakit]

See https://github.com/bigbes/tarantool-php/commits/php7-v2

@Totktonada Is this link correct? I don't see anything related to unix sockets there.

[Totktonada]

Yep. See bigbes@35daa0a and bigbes@bf6ef57.