Fix input fetching script

Retain blank lines in code examples.

The script removed all blank lines from code examples. This is not
always desired as there might be important blank lines inside the code
block. The change targets specifically the starting and ending blank line
of the examples and removes them.

lib/aoc.sh

@@ -26,8 +26,11 @@ echo "Extracting example code blocks..."
 # extract example code blocks
 cat README.md |
   sed -n '/\[code\]/,/\[\/code\]/p' | # extract code blocks
-  sed '/^\s*$/d' | # remove empty lines
-  sed '/^\[\/code\]/d' | # remove closing bracket
+  sed '/\[code\]/{n;d}' | # remove (blank) lines after opening bracket
+  tac | # reverse line order
+  sed '/\[\/code\]/{n;d}' | # remove (blank) lines after closing brackets (preceding blank lines in normal order)
+  tac | # reverse line order again
+  sed '/^\[\/code\]/d' | # remove closing brackets
   sed 's/^    //' | # remove indentation
   csplit - --suppress-matched --elide-empty-files --prefix='input/example' --suffix='%d' '/\[code\]/' '{*}'
 echo "done."