Add [Ignore] parameter 'IgnoreAlways' 

This adds a IgnoreAlways constructor parameter to the [Ignore] attribute
IgnoreAlways will skip the field from getting fetched from the
DbReaderResult so non-existing fields can be properly skiped.

This avoids the extensive amounts of OutOfIndexExceptions to be thown
when the fields is missing from the result set.

I'm open for improvements :)