Create an HDF5 API -> Doxygen function link lookup service

Given an HDF5 API, e.g., `H5Screate_simple`, the service would return `group___h5_s.html#ga8e35eea5738b4805856eac7d595254ae` or [`https://support.hdfgroup.org/documentation/hdf5/latest/group___h5_s.html#ga8e35eea5738b4805856eac7d595254ae`](https://support.hdfgroup.org/documentation/hdf5/latest/group___h5_s.html#ga8e35eea5738b4805856eac7d595254ae)

This would remove tedium from the busy lives of external documentation maintainers.

This service is trivial to implement: it would read the [Doxygen tag file](https://github.com/HDFGroup/hdf5/issues/5593) into a dictionary and service requests from that.