Added ODS writer
Refactored XLSX writer to abstract some pieces into an abstract multi-sheets writer
Created an abstract style helper
Moved shared components around
Invalid names can also be triggered by:
- character ":"
- single quote at the beginning of the name
- single quote at the end of the name
Introduced a StringHelper, wrapping multibyte strings functions
Based on Excel requirements:
- it should not be blank
- it should not exceed 31 characters
- it should not contain these characters: \ / ? * [ or ]
- it should be unique
