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

- go test updated;
- fix typo and `gofmt -s` formatted

added missing imports

Adding more realistic error handling in examples

Open file error return added and UpdateLinkedValue function added to fix linked values within a spreadsheet are not updating.

1) Update readme file credits and go report badge added; 2) Remove use less function; 3) Update test file.

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