Function to get for a record the citation for a given format

[eblondel]

This is not directly invoking the Zenodo API but rather the HTML Zenodo interface to be able to grab the export citation content for a given format. A generic function should be designed taking as arguments the record id and the format. Wrapper functions for each format may be designed.

For scraping html, to investigate if it can be done directly with httr to avoid adding extra dep not required (e.g. scrapeR), unless there is no choice.