autocomplete should be more configurable

[eiked]

The autocomplete helper is a very nice thing,
but I believe it still misses some options to make it even more usable
I believe this can be done at ease.

so currently
autocomplete :table, :field

This currently generates a default query but we might need to customize this.

I'd suggest something around:
autocomplete :table, :scope => :my_scope

(it should then invoke Table.scope to obtain values)

also customization of the limit would be nice,
like
autocomplete :table, :field, :limit => 20

last but not least, adding a block might be cute
like
autocomplete :table, :field {|(name.id)| [name.camelize, id]}

you get the idea

[eiked]

sorry for the typo,
that should have been

autocomplete :table, :field {|(name, id)| [name.camelize, id]}