complete cow school scripts

Move bash scripts under src/bash_scripts, add college/university/smart cow implementations, and mark the completed TODO items.

src/bash_scripts/cow_primaryschool.sh

@@ -0,0 +1,18 @@
+if [[ $# -ne 1 ]]; then
+  echo "usage: $0 <number>"
+  echo "please provide exactly one numeric argument"
+  exit 1
+fi
+
+if ! [[ "$1" =~ ^[0-9]+$ ]] || (("$1" < 1)); then
+  echo "error: argument must be a positive integer"
+  exit 1
+fi
+
+reset
+for ((i = 2; i < "$(($1 + 1))"; i++)); do
+  cowsay "$(($i - 1))"
+  sleep 1
+  clear
+done
+cowsay -e oo -T U "$1"