feature request: implement Literature API features

[laurabrenskelle]

Hello! We are trying to develop python-based usage metrics from OBIS and GBIF for our organization, but it does not look like the pygbif package includes the functionalities for literature metrics from the API. This would be a helpful addition to the package for those interested in investigating the reuse of their datasets.

[CecSve]

Thank you for the suggestion! We would need to add this as a separate module and would therefore require a new version. @jhnwllr - I have added the suggestion to the next version of the package.