support cascade execution of extraction filters in extraction dimension spec

[sirpkt]

This PR fixes #1875

[fjy]

what about cascadeExtractionFn? How should that be used?

edit: okay I see what this is doing

[fjy]

also, can we add an example here with some sample usage?

[sirpkt]

I thought that CascadeExtractionFn is essential to support chaining in current ExtractionFn interface but it is inconvenient to use.
So, I added CascadeDimensionSpec that uses CascadeExtractionFn for only internal use and external input from users is jut array of ExtractionFn s.
However, it receives both CascadeExtractonFn(even though it is only for internal use) and array of ExtractionFn s because of serde, which makes that the patch looks unclear.

[sirpkt]

I understand what you are saying @jon-wei, @drcrallen .
So I'm gonna update the patch that CascadeExtractionFn can have array argument and handle chaining with inner functions.
Then, I can remove CasecadeExtractionDimension.

[jon-wei]

function parentheses/braces styling

[fjy]

@jon-wei @drcrallen more commentz?

[fjy]

it would be really cool if the example showed the dimension value and the final transformed value

[sirpkt]

@fjy I added an example.

[fjy]

👍 after commits squashed

[fjy]

@b-slim @jon-wei any more comments?

[jon-wei]

👍 after squash

[fjy]

@sirpkt will need a CLA: http://druid.io/community/cla.html

you guys may consider filling out the corporate CLA

[fjy]

@sirpkt I can merge this after commits are squashed and CLA is signed

[sirpkt]

commits are squashed.
And also I submitted CLA.