Log Message:
tex-tcolorbox{,-doc}: update to 4.50

- bug fix: 'tcbincludepdf' ignored some raster options
- bug fix: visible seam for 'bicolor' and 'tile' in 'sidebyside' mode
    around the lower (i.e. rightward) part
- Using group around arguments for title in the examples
- Allocate write registers \tcb at out and \tcb at record@out only when needed
- Documentation: recommend to use initialization options after loading hyperref
- Documentation: warn user about white title color becoming invisible
  for the skin 'empty'
- documentation correction
- documentation of library skins is split into a general part and the catalog
  of skins
- '\tcblistof' enhanced to take an optional short title and mimic
  '\listoffigures' where applicable
- library 'skins':
  * new option 'opacitybacklower'
  * new jigsaw variant of 'bicolor':
    'bicolor jigsaw', 'bicolorfirst jigsaw', 'bicolormiddle jigsaw',
    'bicolorlast jigsaw'
  * implementation of bicolor overhauled
  * skin documentation complemented with sidebyside examples.
- library 'theorems':
  * new option 'theorem hanging indent'
- library 'vignette':
  * documentation examples for fading styles for every side added
- library 'raster':
  * '\thetcbrasternum' changed output the content of a counter.
    LaTeX counter 'tcbrasterrow', 'tcbrastercolumn', 'tcbrasternum' documented.