New alteration to support new column

[Seddryck]

It should be possible to create a new column in a result-set based on some static values and based on values of the current row.

<alter>
   <extend identifier="[new column]">
      <script language="ncalc">[ColA] * 4 / Max([ColB], [ColC])</script>
   </extend>
</alter>

The only script language supported is NCalc at this moment.

When using an index identifier the newly created column will be available at the expected position. If the expected position is unreachable (less columns that expected), the alteration will put the new column as the latest column. If the name identifier of the newly created column is already in-use this column will be replaced.

[Seddryck]

Beta available at https://ci.appveyor.com/project/Seddryck/nbi/builds/26918636/artifacts or with version 1.21.0-beta0283.