Add generate_days script

- Add generate_days script to generate templated files for an advent of
  code year.
- Optimize the fetch.sh script (remove awk usage)

fetch.sh

@@ -1,4 +1,4 @@
-#/bin/sh
+#!/bin/sh
 
 if [ ! -e cookies.txt ]; then
     echo "No cookies.txt file exists"
@@ -8,11 +8,11 @@ fi
 list=$(find -name "Day*.cpp" | awk -F '/' '{print $3 "/" $4}' | awk -F '.' '{print $1}' | sed 's/Day//g' | sort)
 
 for item in $list; do
-    year=$(echo $item | awk -F '/' '{print $1}')
-    day=$(echo $item | awk -F '/' '{print $2}')
+    year=${item%/*} # remove everything before /
+    day=${item#*/}  # remove everything after /
     dir="res/$year/day$day/input.txt"
     if [ ! -e $dir ]; then
-        webitem=$(echo $day | sed 's/^0//g')
+        webitem=${day#0}
         echo "Fetching $dir"
         tmp_file=$(mktemp)
         HTTP_CODE=$(curl -s -w "%{http_code}" -o "$tmp_file" --cookie cookies.txt https://adventofcode.com/$year/day/$webitem/input)