add select_all function

usage: 

  				res = Spends\select_all {
  					fields: {
  						single: {
  							"carrier_type_id"
  						}
  						count: {
  							"cost_usd"
  						}
  						text: "sum(cost_usd) as sum"
  					}
  					where: {
  						in: {
  							carrier_id: {1, 2}
  						}
  						range: {
  							month: {
  								{
	  								begin: 10
	  								end: 11
  								},
  								{
  									begin: 20
  									end: 21
  								}
  							}
  							year: {
  								{
  									begin: 2013
  									end: 2014
  								}
  							}
  						}
  					}
  					group_by: {"carrier_type_id"}
  					order_by: {carrier_type_id: "desc"}
  					limit: 10
  					offset: 0
  				}

result SQL query:

SELECT count("cost_usd") as "cost_usd", "carrier_type_id", sum(cost_usd) as sum FROM "spends" WHERE carrier_id in (1, 2) AND ("month" BETWEEN 10 AND 11 OR "month" BETWEEN 20 AND 21) AND ("year" BETWEEN 2013 AND 2014) GROUP BY "carrier_type_id" ORDER BY "carrier_type_id" desc LIMIT 10 OFFSET 0