feature: can specify alias in SQL::Maker#select
join condition accepts Hash
Add document about \%opt for insert() method.
add documents for specifying alias in select method
add document for hash condition of add_join
Merge pull request #23 from debug-ito/master

Documentation about \%opt for insert() method
Merge pull request #20 from Songmu/feature/join-hash-condition

join condition accepts Hash
Merge pull request #22 from Songmu/feature/maker-select-alias

feature: can specify alias in SQL::Maker#select