- descriptions in builtins.go of the form "// attr value"
  - shorted all description attribute names to 4 letters
  - removed fun/Describe-builtins.sh in the process
  - related shell script and Makefile Umbau
  - renamed alldocs.txt to FUNCDOCS.txt to make it stand out better
  - other, minor renamings
  - all *_.* in the tree are build products and will be cleaned

this eliminates the need to edit the awkward register calls by hand
and leaves us with more or less self-explanatory desciptions