Now supporting things like: RNA(ViennaRna::Global::Rna.generate_sequence(20), :empty, fold: { d: 0 })
-- The first parameter to RNA initialization objects (which expects a sequence) can be an Rna object itself, in which case the sequence is extracted.
-- The structural parameters accept hashes now. This is really only used for generating MFE structures with different dangle flags, and as such the resulting object has obj.mfe_rna.structure called on it. This can be abstracted (probably by having a generic result RNA for things like eval / fold / etc.) but let's wait until we want to use it a different way first.

R module supports vertical lines on the histogram plots (for indicating a sample of interest within a distribution) and fonts are more reasonably scaled so the text isn't gigantic.