Implement helpers for literature coercions

[amoeba]

We often want to document a citation to another resource in our EML documents and EML supports this with its literature module. That said, this is very hard to use without some sort of helpers. EML supports coercions from non-EML types to EML types and for literature, we should be able to convert from other formats like BibTeX to generate the entire literature XML tree.

• Figure out what's possible
• Add helpers where/if necessary
• Add documentation somewhere on how to use these, ideally improving the EML package documentation along the way

[rachelsun97]

According to the documentation for eml-literature module written here, we can manually add the bibtex element directly into the EML as of version eml2.2.0. So this ticket may be deprecated