Add include_pattern

[masaruh]

There are cases where it's easier to specify include pattern rather than exclude_pattern (and specifying prefix doesn't work when they share the same prefix).

It would be useful if s3 input has include_pattern. Something like:

             :
    elsif @exclude_pattern.nil? || filename !~ Regexp.new(@exclude_pattern)
        if @include_pattern.nil? || filename =~ Regexp.new(@include_pattern)
            return false
        else
            return true
        end
    else
      return true
             :

[eye8]

This is a useful feature. Although lacking it will not cripple us in our work, it definitely make many thing easier. Thank you.

[rodrigocmn]

This is definitely a very useful feature. Do you guys have any plans to implement it anytime soon?