Create a two-way OBF converter

[willwade]

OBF.

See https://github.com/CoughDrop/obf/tree/master/lib/obf

Basically need a two-way conversion

I.e. Pasco format trees to OBF - and OBF to pasco format trees.

NB: Pasco doesnt support a LOT of OBF's features like images but it does support:

• Sound files
• Links (Links in pasco are sub-trees).
• Cues (in a way. See docs "Different Sound than Labelled" - uses the "vocalization" tag - which doesnt feel the right term)