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

[Songmu]

It can be specified column alias as follows.

$builder->select( 'foo', [ 'foo', [bar => 'barbar'] ] );

[tokuhirom]

You should document it.

[Songmu]

done.

[Songmu]

SQL::Maker::Select->add_select($column, [$alias]) already exists,
but it seems there is no route to call it from SQL::Maker->select, then
I wrote this interface.

[Songmu]

Thank you!