Font retention #33

Documents should export in the same font as the original as much as possible; where the original font was not available for inclusion in the tool i.e. it has a none-free licence the font used should be similar in appearance. This could be achieved by using a font substitution table (like in LibreOffice).

In certain scenarios, where a font is unknown (not in the substitution engine) or the original was OCR or similar, a font recognition engine e.g. https://github.com/robinreni96/Font_Recognition-DeepFont would be useful - although given the scenarios above the software would only need something clever enough to substitute a visually similar font.