Add inner, right, full joins
Merge pull request #3 from m2ym/topic/joins

Add inner, right, full joins
(refs #4) Allow AS operator to take sql-statement.

(select ((:as (select 1 (from :foobar)) :value)) (from :foobar))
;=> #<SXQL-STATEMENT: SELECT (SELECT 1 FROM `foobar`) AS `value` FROM `foobar`>