Added new color toning method "L*a*b* regions"

Allows to specify various "regions" of the image with masks, and to correct
for hue, saturation and lightness.

Inspired by the existing L*a*b* grid (in turn taken from darktable)

rtengine/CMakeLists.txt

@@ -128,6 +128,7 @@ set(RTENGINESOURCEFILES
     vng4_demosaic_RT.cc
     ipsoftlight.cc
     guidedfilter.cc
+    iplabregions.cc
     )
 
 if(LENSFUN_HAS_LOAD_DIRECTORY)