[chlog] Update CHANGELOG ()

Merging branch 'chlog'  into 'main'.

See merge request !1133

CHANGELOG

@@ -15,9 +15,14 @@ BornAgain-1.20?
     * Remove unused/undocumented functions Layer::setThickness, setMaterial
     * Remove rudimentary MPI support (inform us if this is needed)
   > GUI changes:
+    * New representation of sample model (tabular instead of freely wired)
     * Executable renamed to bornagain, except under Windows, where it is still BornAgain
     * Support "*.001" files generated by Nicos at SANS-1 of MLZ / FRM2
     * Improved file chooser for 2d data import
+  > Documentation:
+    * Preserve old web docs (starting with 1.19) as web site now supports multiple versions
+    * Move versioned part of the web docs to this source repository, directory hugo/
+    * Start migrating API documentation to human edited web docs instead of Doxygen
   > Bug fixes:
     * Correct intensities when source or sink is below the horizon (alpha_i or alpha_f < 0,
       thanks to issue raised by Karolina Mothander)