added perl_require and perl_modules

Added two new directives to be used with http://nginx.org/en/docs/http/ngx_http_perl_module.html: perl_modules and perl_require

Example:
use Test::Nginx::Socket;

perl_modules("perl_modules /home/irocha/perl/nginx;");
perl_require("perl_require test.pm;");

repeat_each(1);
plan tests => $Test::Nginx::Socket::RepeatEach * 2 * blocks();
$ENV{TEST_NGINX_ERROR_LOG} = "/tmp/test.log";
log_level('warn');
run_tests();