18.7.7 Methods:

   CLARK       A minor/major cycle cleaning using FFTs for speed
               Fast, but less stable than others.
   HOGBOM      The basic deconvolution method, working component per
               component. Very robust, but possibly Slower than CLARK
   GAUSS       A multi-resolution Clean method using point sources and
               Gaussian sources of different sizes. Slower than HOGBOM,
               but better at recovering all scales.
   MRC         A dual-scale multi-resolution Clean working on a smooth
               and a difference map. Fast, but with no notions of Clean
               component.
   MULTISCALE  A 3-scales multi-resolution-Clean working on 3 smoothed
               versions of the map. Slow, but very stable and adapted to
               sources with extended structures. GAUSS is faster.
   SDI         A major-cycle only method. Good for extended structures
               but not very performant overall.