- Partial logic performance optimization, use pointer reference instead of a pass the variable value;
- Add comments for content types struct definition;
- Update go test `TestSetBorder` section

- Function parameter code is simplified;
- Fix element `Tint` value parsing error in worksheet;
- Update go test

- Improved performance when reading large files, call Token to read tokens one by one instead Unmarshal. Related issue #20 ;
- Fix go test typo;
- Update README

Make functions: `SetCellValue`, `SetCellInt`, `SetCellHyperLink`, `SetCellFormula`, `GetCellValue` and `GetCellFormula` to support the merged cells.

- Character limits for cells added;
- Update go test and fix typo

- Add escape characters of sheet name;
- Update go test and fix typo

- Fix `GetCellValue` causes panic in some particular situation issues;
- Go test updated

- Optimisation code use fmt package
- Update README
- Remove useless function