Visualising non-canonical RNA basepairs

[AntonPetrov]

Great work on the RNA 2D visualisation! Here is a feature request: it would be good to add an option for visualising non-canonical RNA basepairs using the Leontis-Westhof nomenclature.

This functionality exists in Varna, although Varna requires Java.

Non-canonical basepairs can be used for visualising RNA 3D motifs like this sarcin-ricin internal loop:

I am sure it's on your radar but I thought I'd submit an issue anyway.