added README.md
added \Sql\Sql, \Sql\Exception
added where() and wheres() and values()
added order()
added selectOne()
modified README
added update(), set() and sets()
added orWheres()
added delete()
added insert()
set()の値にnullを許可
SET時のカッコを排除
added column()
column()にalias対応
set()の内部仕様変更
insert()仕様変更
insert()仕様変更
JOIN対応
set()とwhere()に文字列を指定するとvalues()の順番が狂う問題を修正
added count()