title: Jquery datatables column search case unsensitive
body: <p>this is my scenario:
  I have a datatable that I initialize in this way:</p>
  
  <pre><code>invoicesDataTable = $('#invoicesDataTable').DataTable({
  
                  processing: true,
                  serverSide: true,
                  searchDelay: 1000,
                  search: {
                      caseInsensitive: true
                  },
                  ajax: {
                      type: 'GET',
                      url: '{!! route("admin.invoice.filterData") !!}',
                      dataSrc: function (response) {
                          return response.data;
                      }
                  },
  //              aLengthMenu: [ [ 50, 100, 150, 200, -1 ], [ 50, 100, 150, 200, 'All' ] ],
                  columns: [
                      {data: 'document_number', name: 'invoices.document_number', orderable: false},
                      {data: 'document_type', name: 'invoices.document_type', orderable: false},
                      {data: 'tax_regime', name: 'invoices.tax_regime', orderable: false},
                      {data: 'auction_id', name: 'auctions.auction_id', orderable: false},
                      {data: 'business_name', name: 'customers.business_name', orderable: false},
                      {data: 'total_amount', name: 'invoices.total_amount', orderable: false},
                      {data: 'datetime_invoice', name: 'invoices.datetime_invoice', orderable: false},
                      {data: 'actions', name: 'actions', orderable: false, searchable: false}
                  ],
              });
  </code></pre>
  
  <p>After initialization I add search on each column in this way:</p>
  
  <pre><code>$('#invoicesDataTable thead th').each(function () {
              var title = $(this).text();
              $(this).html('&lt;input type="text" style="width:100%;" placeholder="' + title + '" /&gt;');
          });
  
          invoicesDataTable.columns().every(function () {
              var that = this;
              $('input', this.header()).on('keyup change', function () {
                  if (that.search() !== this.value)
                      that.search(this.value, false, true, true).draw();
              });
          });
  </code></pre>
  
  <p>It works correctly except for case insensitive search. If I have a column with value like "John" and I search for "john" it doesn't show to me the row with "John". There is a way to make it works?
  (The global search works perfectly in case insensitive way)</p>