A few updates, cleanup updated weather module.

modules/calculate/calculate.sh

@@ -1,5 +1,15 @@
+#!/usr/bin/env bash
 [ -f functions.sh ] && source functions.sh
 
+# Dependencies required by this module
+dependencies=("calc")
+
+# Check dependencies before running
+if ! check_dependencies "${dependencies[@]}"; then
+    msg "$2" "$1: This module requires: ${dependencies[*]}"
+    exit 1
+fi
+
 calculate() {
     calc -- "$*" | tr -d '[:space:]'
 }