The inline string struct is actually the same
as the shared strings struct, reuse it.

Note that Go version 1.10 is required.

Fixes #462

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

- Update import PKG syntax in struct;
- Update test XLSX file (include table, charts, functions, comments and hyperlink on Sheet1)

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