Introduce a Reader range

[madflow]

This PR introduces a range for readers like discussed here: #561 (comment)

The range can be defined on a Reader by setting a zero based start - and end column index. This can be done before or after a reader has been opened.

The reader will only yield data starting at the start index - and stop reading after the end index.

If an end index is provided missing cells are filled with empty values so there is always the same range.

Given the CSV:

'csv--11', 'csv--12', 'csv--13'
'csv--21', 'csv--22'
'csv--31'

$reader->open($csv);
$reader->setStartColumnIndex(0);
$reader->setEndColumnIndex(1);

Outputs:

array(3) {
  [0]=>
  array(2) {
    [0]=>
    string(7) "csv--11"
    [1]=>
    string(7) "csv--12"
  }
  [1]=>
  array(2) {
    [0]=>
    string(7) "csv--21"
    [1]=>
    string(7) "csv--22"
  }
  [2]=>
  array(2) {
    [0]=>
    string(7) "csv--31"
    [1]=>
    string(0) ""
  }
}

I only did this for the CSV reader for RFC purposes.

[boxcla]

Verified that @madflow has signed the CLA. Thanks for the pull request!

[madflow]

Maybe naming the exposed setter "setRange" and keeping the column indexes internal would be a better option...?

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[madflow]

I have no plans on working on this PR anymore. Closing...