Fix column index in ActiveExcelSheet

Merge pull request #45 from devOp1/master

Fixed column numbering on setCellValue() to 1-based

Merge pull request #44 from devOp1/master

Replaced PhpExcel with PhpSpreadsheet

Merge pull request #27 from codemix/26-non-db-attributes

Issue #26 Fix error for non-DB attributes

Merge pull request #22 from pana1990/21-related-model

fix #21

Make modelInstance configurable

Issue #18 Push min requirement to Yii 2.0.13

Implement beforeRender and afterRender events

Add startRow/startColumn to ExcelSheet

Update README