Use declare builtin to show variables in debug_var()

src/include/mkit.sh

     #
     $MKIT_DEBUG || return 0
     local __mkit_debug_var_name__       # variable name to debug
+    local decl                          # declare string
     for __mkit_debug_var_name__ in "$@"; do
         {
-            echo -n "MKIT_DEBUG: ${FUNCNAME[1]}():"
-            echo -n " $__mkit_debug_var_name__"
-            echo -n "='${!__mkit_debug_var_name__}'"
-            echo
+            decl=$(declare -p "$__mkit_debug_var_name__")
+            decl=${decl#declare ?? }
+            echo "MKIT_DEBUG: ${FUNCNAME[1]}(): $decl"
         } >&2
     done
 }