Pandoc has no PDF export

[StuartJMackintosh]

Can't select PDF for Pandoc export.
Required as standard CodiMD export does not support the additional modules (ie Mermaid, Graphviz) whereas Pandoc (with filters) does.

https://github.com/Hakuyume/pandoc-filter-graphviz
https://github.com/timofurrer/pandoc-mermaid-filter

[Sieboldianus]

This is strange because in the original PR #1273, support pandoc pdf export is crossed, as if finished.