Convert many RGL modules from Latin-1 to UTF-8 to speed up compilation

Also add flags coding=utf8 to silence warnings.

src/abstract/Construction.gf

@@ -1,4 +1,5 @@
 abstract Construction = Cat ** {
+flags coding=utf8 ;
 
 -- started by AR 6/12/2013. (c) Aarne Ranta under LGPL and BSD