Doc: added Flagging section and flag description tables in Windowed measurement and Weighting sections.

Doc: added a first batch of model-fitting parameters to the list of measurements.

Doc: Added :param: role for SExtractor measurements parameters and modified custom CSS to manage the :param: role.
Doc: Added targetparam class and setup targets in preliminary measurement parameter list.

Doc: Customized CSS to have equation permalinks visible when hovering the mouse.

Doc: removed non-compliant characters in citation labels that would create problems with Sphinx v1.6+ (see https://github.com/sphinx-doc/sphinx/issues/3917).

Fixed tests.

Fixed sincosf() warning.

Replaced doc PDF with (very preliminary) Sphinx source.
Pushed version number to 2.24.

Added more complete headers to all files.
Clarified licensing issues.
Updated FITS library.
Updated configuration files.
Added configuration files to the list of data that get installed in ${prefix}/share/sextractor.
Added background offset and point-source model components: FLUX_BACKOFFSET,FLUXERR_BACKOFFSET,FLUX_POINTSOURCE,FLUXERR_POINTSOURCE,MAG_POINTSOURCE,MAGERR_POINTSOURCE.
Tweaked model-fitting convergence parameters.
Fixed catalogue source ordering/number issue in dual-image mode.
Pushed version number to 2.13.0.