Save and parse non-text data to/from files

[ryonakano]

At the moment the app saves and parses only text data, but it should also save and parses non-text data like font sizes, whether a font is bold, italicized, or underlined, etc.

[ryonakano]

I think the current file type, CSV, can't save those data, so I suppose we need to create a new own file type (maybe based on CSV) if we address this issue.

[elegaanz]

Even if it is a lot of work, supporting .ODS files would be ideal.