Heuristics to detect proper mime type for XLSX files expect to see
certain files at the beginning of the XLSX archive. The order in which
the XML files are added therefore matters.
Specifically, "[Content_Types].xml" should be added first, followed by the
files located in the "xl" folder (at least 1 file).
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
Added top level methods on the Writer:
- addRowWithStyle()
- addRowsWithStyle()
Added a style builder, to easily create new styles.
Each writer can specify its own default style and all styles will automatically inherit from it.
For now, the style properties supported are:
- bold
- italic
- underline
- strikethrough
- font size
- font name
- wrap text (alignment)
