This directory contains third-party C libraries used by PyFITS.  Currently
there is only one external library used, which is CFITSIO.  The current
version of CFITSIO is 3.30 (though the version can be checked by looking at
cextern/cfitsio/changes.txt).

It should be noted that this directory actually only contains cherry-picked
parts of CFITSIO used to specifically to support image tile compression.  This
does not contain the entirety of CFITSIO.  However, system packagers may remove
this bundled version of CFITSIO and link with a system-installed version
instead.  Please see the top-level README.txt and the comments in setup.cfg to
configure the build for linking with the system CFITSIO.

Note that CFITSIO also includes a complete copy of zlib.  This may also be
replaced in favor of a system version of zlib.
