working with filters

[JO0st]

There is no option to specify using filters (for example (https://github.com/tomduck/pandoc-fignos)(https://github.com/tomduck/pandoc-fignos)).

Adding filters to the pandoc-config.json works, but this feature isn't documented in the file, so it isn't clear that this is possible.

[TAKeanice]

This is the same as #24