ngx_mruby can write nginx build in variable and request variable

Add Nginx::Var#set "nginx internal var", "string val"

- config

        location /check {
            set $fuga "100";
            mruby_set_code $hoge 'Nginx::Var.new.fuga.to_i * 2';
            mruby_content_handler_code '
              r = Nginx::Request.new
              Nginx.rputs "fuga => #{r.var.fuga} "
              Nginx.rputs "hoge => #{r.var.hoge} "
              r.var.set "fuga", r.var.hoge.to_i * 2
              Nginx.rputs "fuga => #{r.var.fuga} "

            ';
        }

- result

$ curl http://127.0.0.1:8000/check
fuga => 100 hoge => 200 fuga => 400