NeXML translation into JSON-LD

[sckott]

idea in collaboration with @cboettig

Idea is to improve integration between Phenoscape and NeXML data by being able to express NeXML as linked data in JSON-LD

the idea would be to get the workflow working here https://github.com/cboettig/nexld in R - then could be deployed elsewhere (e.g., within Phenoscape API perhaps)