Local FITS Conventions supported by FITSIO

In a couple cases FITSIO supports local FITS conventions which are not defined in the official NOST FITS standard and which are not necessarily recognized or supported by other FITS software packages. Programmers should be cautious about using these features, especially if the FITS files that are produced are expected to be processed by other software systems which do not use the FITSIO interface. These local conventions should be considered as prototypes, and they may not necessarily be supported in future versions of FITSIO, especially if an alternative convention is officially adopted by the FITS community.