Chumper/Datatable — pull request #110 by sburkett (2014-06-12 18:30:50+00:00)
Title: Implementation of "Exact Matching" on column-based searches

My first pull-request, so pardon if I miss something here. This one is a fairly self-explanatory addition. Basically, you can use a new `setExactMatchColumns()` method to specify which column names should use exact matching rather than a partial (LIKE) match. This arose out of need, as I wanted most of my columns to be searchable via LIKE expressions, but others to be via exact matching.

Pseudo-example:
```
return Datatable::query($stuff)
->showColumns('id', 'field1', 'field2', 'field3')
->searchColumns(array('id', 'field1', 'field2', 'field3')
->orderColumns('id', ''field1', 'field2', 'field3')
->setExactMatchColumns(array('field3'))
->make();
```